Natural World

Rivers and Streams

The rivers and streams that flow to Lake Superior through Pictured Rocks National Lakeshore have a relatively steep gradient and are rather short, because the peninsular divide in the area is much closer to Lake Superior than to Lake Michigan.

The steep gradient includes waterfalls, where the streams drop over the escarpment. The more prominent waterfalls within the lakeshore are Munising, Miners, Mosquito, Bridalveil, Chapel, Spray, and Sable Falls. Especially noticeable at the waterfalls is the brown color of the water due to humic acids that originate from the wetlands in the headwaters.

The discharge (rate of flow) of the streams is highest in the late spring and early summer following snowmelt. In addition, these streams are very responsive to rainfall, and will rise immediately following a significant rain. Discharge can double for a day or so after a rainstorm.

Miners River is the longest and largest river in the lakeshore. Its discharge near the mouth averages 46 cubic feet per second during June and drops to an average of 21 cubic feet per second in late summer and fall. The Hurricane and Mosquito Rivers have similar discharges during spring and early summer (19 cubic feet per second), but that of the Mosquito River drops more significantly as the summer progresses.

Munising, Chapel, Section 34, Spray, Sevenmile, Beaver, Rhody, Sullivan, and Sable Creeks are shorter and carry less water. Beaver Creek and Grand Sable Creek flow from lakes and have more stable discharges, because the lakes buffer the effects of precipitation.

The substrates of the streams are variously composed of cobble/gravel, sand, and bedrock. The substrate in depositional areas along the banks and upstream from beaver dams is mud/silt. Most pools are formed by the force of water flowing over trees that have fallen into the streams.

The quality of the water of the inland lakes, rivers, and streams is directly related to the watersheds they drain. The majority of the shoreline zone's rivers and creeks have headwaters that occur in the Inland Buffer Zone and the surrounding region. Management of these areas can affect the quality of the national lakeshore's water bodies.

Natural Features & Ecosystems

Pictured Rocks National Lakeshore is located along the south shore of Lake Superior, between the communities of Munising and Grand Marais, in the north woods of Michigan's Upper Peninsula. It was authorized by Congress as the first national lakeshore on October 15, 1966, "

" (P.L. 89-668). The "diminishing shoreline" refers to public access to Great Lakes shores lost to private ownership. Formal establishment of the national lakeshore came on October 6, 1972.

The 71,397 acres of the park are divided approximately equally by the enabling legislation into two distinct ownership and management zones. The federally-owned Shoreline Zone was established for the traditional national park reasons of preserving natural and cultural resources and providing for recreation.

The non-federal Inland Buffer Zone (IBZ) was created "

." Congress intended that the buffer zone serve to preserve the setting of the Lake Superior shoreline and inland lakes, and protect the watersheds and streams. Sustained yield timber harvesting and other resource management activities compatible with preservation and recreational use were permitted in the IBZ. Consumptive resource use, however, was intended to be subordinate to public recreation and the protection of "the usefulness and attractiveness of the lakeshore." The IBZ is comprised of national and state forest land, extensive private commercial forest, and small private parcels.

The park boundary extends one-quarter mile out over the surface of Lake Superior along the length of the park. National Park Service authority is limited to the surface waters within this one-quarter mile.

Lakes and Ponds

Lake Superior is the major water body in the area and forms the northern border of Pictured Rocks National Lakeshore. The lake has a maximum depth of 420 m (1,335 feet) but is relatively shallow near PRNL's shoreline. Its surface lies at an elevation of 187 m (600 feet) above sea level. The maximum tidal/storm elevation has been recorded at 604.3 feet. In recent times lake level has varied on the order of several feet due to changes in precipitation and evaporation.

The more prominent inland lakes are Grand Sable, Beaver, Little Beaver, Chapel, Little Chapel, Miners, Trappers, Legion, Kingston, and the Shoe Lakes. These lakes range in size from 762 acre Beaver Lake to 10 acre Miners Lake. Most of the inland lakes, with the exception of Grand Sable Lake and Chapel Lake, are quite shallow (3 to 6 m, 10 to 20 feet in average depth), but have lengthy flow-through rate times.

Many of the lakes are mesotrophic and have Secchi disk (water visibility) readings between 2 and 5 meters. The intensive logging in the area and recurrent fires may have caused erosion and nutrient deposition in the lakes. Miners Lake and Little Chapel Lake exhibit the greatest trend toward eutrophication. The most oligotrophic lakes are Legion Lake, the Shoe Lakes, and Grand Sable Lake. The inland lakes vary considerably in their water chemistry, but many can be classified as productive, brown, alkaline water lakes.

Although Legion, the Shoe, Kingston, and Trappers Lakes are alike in that they are closed basin lakes (having no streams flowing in or out) they were formed in different ways. Kingston, Legion, and the Shoe Lakes are kettle lakes, formed by the melting of a block of ice that separated from the retreating glacier about 10,000 years ago. In particular, Legion Lake and the Shoe Lakes lie high on the watershed divide between Lake Superior and Lake Michigan and receive very little groundwater input of elements like calcium, magnesium, and silica. They are acidic (pH 4.8-5.1), poorly buffered, and have high Secchi disk readings (5-9 m).

Trappers, Beaver, and Little Beaver Lakes are located in Beaver Basin, which was once an embayment of Lake Superior when the lake level was considerably higher. As the lake level dropped, sandy beach ridges separated the lakes from Lake Superior, creating these relict lakes. Miners Lake lies along the Miners River in Miners Basin, which was also an embayment of Lake Superior during higher lake levels approximately 5,000 years ago.

Chapel Lake is elongate and was likely formed by a large plunge pool in a glacial meltwater channel. Its southern basin is about 43 m (140 feet) deep, extending into the Jacobsville Sandstone, and is shallow toward the northern end, where rooted, aquatic plants emerge at the surface. Chapel Lake is meromictic; the deepest layer of water does not mix with the upper lakewater during spring and fall turnovers. The water below approximately 18 m (60 feet) is cold, dense, and anoxic (extremely limited dissolved oxygen).

Groundwater

The most accessible sources of groundwater over a large part of Alger County are the deposits of glacial drift. These range from clayey till and lake deposits of low permeability to highly permeable sand and gravel outwashes. The most extensive outwash in Pictured Rocks National Lakeshore is the Kingston Outwash Plains. The thickness of the outwash deposits of the Kingston Plains probably exceeds 30 m (100 feet). Some small wells in the area are yielding in the range of 20 gallons per minute (gpm).

Beds of sand that were deposited in glacial lakes also are a source of water for wells. Glacial lake deposits in the Lakeshore occur in a strip along the shore of Lake Superior. Most of the wells tapping the lake deposits are shallow-driven and commonly provide a satisfactory and inexpensive water supply. Ten to twenty gpm can be obtained from properly constructed wells tapping sandy lake deposits, and where outwash or beach-deposited sand and gravel are present, wells may yield 100 gpm.

The Grand Sable Dunes are perched dunes situated at the northeastern end of the national lakeshore. They are located above the groundwater, are not saturated, and thus do not yield water to wells. The dune sands are very permeable, and most of the precipitation falling on them infiltrates to recharge the under-lying aquifers.

The Munising sandstone underlies nearly all of the Lakeshore. This formation forms the most extensive aquifer throughout the area, but it is tapped by only a few wells. This apparent paradox is due to the fact that in most of the area it is overlain by other aquifers that can be tapped at shallower depths.

The Jacobsville sandstone underlies all of Alger County. In much of the county it has little potential as a source of water; however, at Au Sable Point the sandstone is at or near the surface.

The groundwater yielded by outwash and lake deposits, Munising sandstone, and Jacobsville sandstone meets federal primary safe water drinking standards; some of the groundwater contains objectionable amounts of iron. The groundwater from the outwash and lake deposits is soft to moderately hard, whereas Munising sandstone and Jacobsville sandstone water is moderately hard to hard.

Soils

The soils of Pictured Rocks National Lakeshore reflect the area's geologic background, topography, climate, and vegetative influences. The two dominant soil-forming elements are parent material and drainage conditions.

Soil types of the lakeshore can be grouped as upland loams, plains sands, sandy loams and sands, upland stony loams and sands, lakeshore soils, swamp and wetland soils, and organic soils.

Upland loam soils are underlain by gravels at 15 to 30 cm (6 to 12 inches), with stony clays below gravel. They are generally well drained in surface layers and are moderately productive. The soils are distinguished by large amounts of limestone in the lower gravels. Local areas are stony. Upland loams occur in the southwestern portion of the lakeshore.

Most of the plains sands occur in land that is level to slightly rolling. All these soils are underlain by dry loose sand several feet deep. These soils are well drained and low in fertility. Plains sands occur throughout the Kingston Plains and extend into the southeastern and southcentral portions of the inland buffer zone.

Hilly terrain and stony conditions occur throughout the sandy loams and sands soils. The surface soils, 30 to 40 cm (12 to 16 inches) deep, are underlain by leached sands, which are easily penetrated. Some clays occur locally in the subsoil. Sandy loams and sands soils occupy the comparatively high, hilly upland areas in the eastern sections of the lakeshore, in the western portion of Beaver Basin, and southwest of Sand Point.

Bedrock (sandstones and limestones away from Lake Superior) is present at slight depth throughout upland stony loams and sands. The profile is poorly developed, stones are very common, and many inclusions of clay and clay hardpan are present. Upland stony loams and sands soils are present in the rolling terrain from Beaver Lake to Sand Point.

Sand, gravels, and stones are indicative of lakeshore soils. They are generally excessively dry due to rapid subsurface drainage. Active and stabilized dune areas are included. Lakeshore soils occur at Sand Point and extensively along the northern shore of the national lakeshore from Miners Beach to Sable Creek.

Swamp and wetland soils have black muck surface layers with clay or sand beneath. The water table is from .3 to 1 m (1 to 3 feet) below the surface, and the soils are almost permanently waterlogged. Water-tolerant trees, shrubs, and herbaceous plants grow well in these soils. Swamp and wetland soils are present in bogs, marshes, and in narrow floodplains along major stream channels.

Organic soils are mucks and peats up to ten feet deep. Water-tolerant vegetation grows well in this soil type.

Insects

What's Biting You?
An outdoor adventure at Pictured Rocks National Lakeshore is an exhilarating experience but, at certain times of the year, our visitors can be distracted by the smallest inhabitants of the north woods: the biting flies.

Earliest to appear on the scene in mid-spring are the mosquitoes and black flies. The female mosquito, as with most biting flies, is the one doing the biting. She requires a blood meal in order to get enough protein for her eggs to develop properly. Most male biting flies feed on pollen or nectar from flowers. Male mosquitoes have feathery antennae and live about one week. Mosquitoes lay their eggs in calm or standing water, and the larvae are aquatic. Many diseases are transmitted by mosquitoes, and it is best to avoid their bites as much as possible.

Black fly larvae are also aquatic, but prefer to live in running water like streams or rivers. Black fly larvae attach themselves to rocks in the stream by a suction cup on their tail end, and filter out food particles from the water with their feathery fan-like structures around their mouths. After pupation, the adult black fly rides on a bubble of air to the waters surface and flies out of the water. The adult females are vicious biters, but luckily, North American black flies do not transmit disease to humans.

Seldom seen or heard but sometimes felt is the No-See-Um, also called Punkies or Biting Midges. No-See-Ums resemble miniature, short-legged mosquitoes, and are usually less than 3 millimeters long. Only females of a few species bite humans. The majority bite other insects or eat nectar. Their larvae are mostly aquatic and are scavengers or predators. No-See-Ums that bite humans are less common than other biting flies in Pictured Rocks.

Deer flies and horse flies appear by mid-summer, generally when the mosquitoes and black flies decrease in number. Deer flies have brightly colored eyes and patterned wings, and come in a variety of different types. The much larger horse flies are more drab brown or black, sometimes with light spots, and clear wings. Horse flies have large, dark or green colored eyes. Females of both deer and horse flies fly in noisy, fast circles around their chosen victim, and can inflict a painful bite. Their predaceous larvae are aquatic as well, and can live in both lakes and streams.

The stable fly is the biting fly at the Pictured Rocks beaches in mid to late summer. It is a relative of the house fly, but it bites. Its body is grey, with a distinctive checkerboard pattern on the abdomen. It is commonly referred to as the 'beach fly or black fly' and prefers to bite its victim's legs and ankles. Both the male and female stable fly bite, but they also feed on pollen. Unlike the other biting flies, the larvae of the stable fly are terrestrial, and live in and eat decaying vegetation. Stable flies are not known to transmit disease in humans, but are annoying enough to drive people away from beaches when they are numerous.

It is always best to play it safe and avoid being bitten by biting flies. Use protective clothing or insect repellant, and carry an allergy medicine or anti-histamine in case of an allergic reaction to a bite.

References:

Borror, D. J. and White, R. E., Eds. 1970. The Peterson Field Guide Series, A Field Guide to Insects: America north of Mexico. Houghton Mifflin Company, Boston, New York. 404 pp.

Milne, L. and Milne, M. 1997. National Audubon Society, Field Guide to North American Insects & Spiders. Alfred A. Knopf, Inc., New York. 989 pp. Merritt, R. W. and Cummins, K. W., Eds. 1984.

An Introduction to the Aquatic Insects of North America, Second Edition. Kendall/Hunt Publishing Company, Dubuque, Iowa. 722 pp.

Written by Amy E. Maskey, 8-7-2006

NATURE & SCIENCE

Towering above Lake Superior are the most prominent of the lakeshore's geographic and scientific features, the multicolored sandstone cliffs for which the lakeshore is named. These cliffs reach to a height of 200 feet above the lake and extend more than 12 of the 42 miles of shoreline within Lakeshore boundaries. Equally important as these cliffs in geographic and scientific significance are the Grand Sable Dunes, sand dunes perched atop five square miles of high sand bluffs at the eastern portion of the Lakeshore. Miles of unspoiled beaches are a third prominent feature of the lakeshore.

The scientific features of the lakeshore reach far beyond the visually spectacular. Because of its location within the transition zone between the boreal and eastern deciduous forest biomes, the Lakeshore has elements of both forest types. Hardwood forests are prevalent, but conifers dominate some sites. Soils range from well-drained sandy soils to hydric soils. Wetlands are common throughout the Lakeshore. Many wildlife species live permanently or seasonally within the Lakeshore. The cold maritime climate along the shore of Lake Superior greatly influences physical conditions and hence biotic communities.

Plants

Plant life within and adjacent to the Lakeshore is varied. Upland forests of beech, hemlock, and maple are found on well drained sandy soils.

Wetland soils that have developed since the retreat of the most recent glacial recession give rise to spruce, tamarack, alder, and white cedar communities. Streams and lakes are ringed with alder and striped maple. The Grand Sable Dunes are a rare collection of habitats with jack pine pockets, willow, the federally threatened Pitcher’s thistle (Cirsium pitcheri), Lake Huron tansy (Tanacetum huronense), and several species of grape ferns, including four state threatened species of Botrychium.

Aquatic macrophytes and those that are emergent from the water surface provide habitat for algae, protozoa, invertebrates, and fish. There are 76 plants that are generally categorized as aquatic in the park’s waters. The smallest plants of Pictured Rocks National Lakeshore include hundreds of taxa of algae including dinoflagellates (Pyrrhophyta), yellow-brown algae (Chrysophyta), diatoms (Bacillariophyta), and green algae (Chlorophyta). Seasonal fluctuations occur in the relative densities of these unicellular plants.

Dominant diatoms include Asterionella formosa, Fragillaria intermedia, Aulocoseira islandica, and Tabellaria fenestrate. The filamentous green alga, Bulbochaete sp., is found attached to submerged logs in softwater Legion Lake. Diatoms of this acidic lake are typically benthic, and, due to limited dissolved silica, the cells walls are not preserved in the sediments. Shapely desmids (Chlorophyta) also occupy this lake.

Trees and Shrubs

Pictured Rocks lies within the northern hardwood/hemlock/white pine region of the eastern deciduous forest. This forest type is transitional between the more homogeneously deciduous forests to the south and the coniferous boreal forests to the north.

About 80 percent of the lakeshore is dominated by upland northern hardwoods. Dominant species are beech (Fagus americanus), sugar maple (Acer saccharum), red maple (Acer rubrum), yellow birch (Betula allegheniensis), hemlock (Tsuga canadensis), and white pine (Pinus strobus).

On coarse outwash and coastal sands (about 10 percent of the Lakeshore), red pine (Pinus resinosa), white pine and jack pine (Pinus banksiana) are dominant. Successional stands within these soils contain considerable amounts of paper birch (Betula papyrifera) and aspen (Populus tremuloides). Ground and crown fires influenced this pine-dominated vegetation prior to European settlement.

Scattered small patches of wetter habitat occur on upland benches and in poorly drained topographic lows (about 10 percent of the Lakeshore). These contain boreal forest elements such as black spruce (Picea mariana), white spruce (Picea glauca), white cedar (Thuja occidentalis), and larch (Larix laricina). Larger white cedar glades within the national lakeshore are southwest of Grand Sable Lake, south of Au Sable Point.

Freshwater Plants

The phytoplankton of the inland lakes of Pictured Rocks National Lakeshore include at least 51 taxa of blue-green algae (Cyanophyta), dinoflagellates (Pyrrhophyta), yellow-brown algae (Chrysophyta), diatoms (Bacillariophyta), and green algae (Chlorophyta). Seasonal fluctuations occur in the relative densities of these unicellular plants.

Dominant taxa include the diatoms Asterionella formosa, Fragillaria intermedia, Aulocoseira islandica, and Tabellaria fenestrata and the blue-green algae Aphanizomenon flosaquae, Aphanocapsa rivularia, Chroococcus limneticus, and Lyngbya birgei. The filamentous green alga, Bulbochaete sp., is found attached to submerged logs in softwater Legion Lake. Diatoms of this acidic lake are typically benthic, and, due to limited dissolved silica, are not preserved in the sediments.

Birds

Habitat for the federally listed endangered Piping Plover (Charadrius melodus) is found within the Lakeshore. Plovers have nested within the park, most recently in the early 1990's in Grand Marais on the beach north of the Grand Marais Ranger Station. However, the nest was vandalized, and plovers have not nested on park lands since.

Nesting habitat for the Peregrine Falcon (Falco peregrinus), a State of Michigan Endangered species, is also found in the Lakeshore. Peregrine Falcons were released in the Lakeshore in 1989 and 1991 as part of a Midwest peregrine reintroduction program and have nested successfully in the park for several years since, as well as on nearby Grand Island.

The Bald Eagle (Haliaeetus leucocephalus) nests within the Lakeshore. Three nest territories are known.

State-listed avian species present in the Lakeshore include Common Loon (Gavia immer), Red-shouldered Hawk (Buteo lineatus), Cerulean Warbler (Dendroica cerulean), and Osprey (Pandion haliaetus).

There have been 176 species of birds documented at the Lakeshore. Some reside in the park all year, some are present only in the summer, and others are only observed during migration.

Avian species of interest found within the Lakeshore include upland species such as Ruffed Grouse (Bonasa umbellus), Spruce Grouse (Dendragapus canadensis), Sharp-tailed Grouse (Tympanuchus phasianellus), and American Woodcock (Scolopax minor); as well as wading birds and waterfowl, including Sandhill Crane (Grus canadensis), Great Blue Heron (Ardea herodias), and several species of the orders Anseriformes (geese, ducks and mergansers), Podicipediformes (grebes), and Charadriiformes (gulls and shorebirds). Grouse and woodcock are popular species with Upper Peninsula hunters.

Besides the previously mentioned threatened or endangered species (Bald Eagle, Peregrine Falcon, Merlin and Osprey) several species of raptors are found within the park. These species include Northern Goshawk (Accipiter gentilis), Northern Harrier (Circus cyaneus), Sharp-shinned Hawk (Accipiter striatus), Red-tailed Hawk (Buteo jamaicensis), Barred Owl (Strix varia), and other hawk and owl species.

Other common avian species include Turkey Vulture (Cathartes aura) with its slightly V-shaped appearance while soaring, several species of Orders Piciformes (woodpeckers) and Passeriformes (perching birds), including numerous warblers and other songbirds.

Amphibians

As would be expected at this northern latitude, herpetofauna are not numerous. Only 5 reptilian and 11 amphibian species are known to exist within the Lakeshore.

Among species present are American toad (Bufo americanus), spotted salamander (Ambystoma maculatum), spring peeper (Hyla crucifer), leopard frog (Rana pipiens), painted turtle (Chrysemys picta), snapping turtle (Chelydra serpentina), eastern garter snake (Thamnophis sirtalis), and northern redbelly snake (Storeria occipitomaculata).

Animals

Though animal life is abundant within the Lakeshore, visitors often do not see many animals during their visit beyond chipmunks and perching birds. A walk down park trails may reveal bear scat, a pile of pine cone bracts from a feeding red squirrel, or the chatter of a chipmunk.

Animal life in this varied habitat of wetland, sand dune, cliff, and northern hardwood forests includes white-tailed deer, black bear, wolves, and an occasional moose. Smaller animals include a variety of migratory and nesting perching birds as well as bald eagle, osprey, raven, and barred owl and broad-winged hawks. Fisher, mink, marten, beaver, skunk, red squirrel, and numerous species of small mammals such as shrews and mice inhabit various Lakeshore habitats.

Other Invertebrates (corals, sponges, worms, etc.)

Zooplankton communities vary among the lakes. In addition, these communities vary seasonally and with depth within the same lake. To date, 35 taxa of cladocerans, 11 species of calanoid and cyclopoid copepods, and two genera of rotifers have been identified from eight lakes in Pictured Rocks National Lakeshore.

As is typical, one cladoceran species, one calanoid copepod species, and one cyclopoid copepod species dominate the zooplankton community in a lake, with other species occurring at much lower relative frequencies. Dominant zooplankton taxa include the cladocerans Bosmina longirostris, Eurycercus lamellatus, Daphnia galeata mendotae, Holopedium gibberum, and Pseudochydorus globosus; the calanoid copepods Skistodiaptomus oregonensis, Epischura lacustris; the cyclopoid copepods Cyclops vernalis and Diacyclops bicuspidatus thomasi; and rotifers of the genus Keratella.

Mammals

The federally endangered gray wolf (Canis lupus) is found occasionally within the Lakeshore during snow-free seasons; however, no established individuals or packs are known to reside in for any length of time or breed in the park.

Other mammals of interest include moose (Alces alces), lynx (Lynx canadensis), red fox (Vulpes vulpes), river otter (Lutra canadensis), fisher (Martes pennanti), badger (Taxidea taxus), star-nosed mole (Condylura cristata), and beaver (Castor canadensis).

Moose are uncommon in the Upper Peninsula due to the meningial worm transmitted from deer, and are rarely seen in the lakeshore. Lynx are uncommon.

Otter, marten, and fisher were virtually extirpated in the area but have made a comeback. Badger expanded their range from the western prairies as settlement cleared forests; records in the Upper Peninsula are rare. Beaver are common and are important for the major changes their activities have on the forest ecosystems near streams.

Other common mammals include black bear (Ursus americanus), coyote (Canis latrans), bobcat (Lynx rufus), white-tailed deer (Odocoileus virginianus), mink (Mustela vison), muskrat (Ondatra zibethicus), skunk (Mephitis mephitis), raccoon (Procyon lotor), snowshoe hare (Lepus americanus), porcupine (Erethizon dorsatum), and eastern chipmunk (Tamias striatus). Bear and deer are the primary prey species for Upper Peninsula hunters. Porcupine frequently attack park structures, seeking minerals from plywood and salt-impregnated wood.

Extirpated mammalian species include caribou (Rangifer tarandus) and wolverine (Gulo gulo). Caribou historically ranged throughout the Upper Peninsula, but were rare by 1850 and last seen around 1910 probably disappearing due to habitat changes brought about by human activity.

Fish

The lakes and streams of Pictured Rocks National Lakeshore support populations of cool water game fish and trout, and can supply a limited amount of fish for angler consumption. Major cool water game species include smallmouth bass (Micropterus dolomieui), northern pike (Esox lucius), walleye (Stizostedion vitreum), yellow perch (Perca flavescens), and non-native smelt (Osmerus mordax).

Typical trout species found in the lakeshore are brook trout (Salvelinus fontinalis), lake trout (Salvelinus namycush), and non-native rainbow trout or "steelhead" (Salmo gairdneri). The white sucker (Catostomus commersoni), common in the diet of Bald Eagles, a variety of minnows, darters, sculpin and dace, and sun fish are also common.

In all, 59 species are present in Lakeshore waters. From 1997 to 2005 coaster brook trout, a life form variant of brook trout that spends much of its life cycle in Lake Superior, was experimentally re-introduced in the Mosquito River, Sevenmile Creek, and Hurricane River, in concert with a Lake Superior-wide restoration program. Research is providing data about the movement of brook trout and their stream habitats.

Prior to the establishment of the national Lakeshore, many species were stocked into (including non-natives) and removed from waters of the area by the Michigan Department of Natural Resources. The NPS is now seeking to manage for a more natural fishery, and stocking of fish no longer occurs.

Geologic Formations

Geological history recorded in the sedimentary rocks and surficial deposits of Pictured Rocks National Lakeshore is limited to two widely separated intervals of geologic time, the Late Precambrian, Cambrian, and Early Ordovician Periods (500-800 million years before present) and the Late Quaternary Period (two million years before present to the present).

During the Cambrian and Early Ordovician periods, sediments were deposited in the shallow seas and near-shore deltas that covered what is now northern Michigan. These deposits became the sandstone units that are exposed within the Lakeshore. Except for their exposure near Lake Superior, these units are presently covered by a veneer of Quaternary glacial drift.

Bedrock is best observed in the western one-third of the Lakeshore where cliffs rise up to 60 m (180 feet) from Lake Superior. These extend along the lake about 27 km (17 m) from Munising to Beaver Basin. For a short distance inland from the escarpment, bedrock is occasionally exposed.

The Jacobsville Formation, of Late Precambrian age, is the oldest formation exposed in the lakeshore. It is a fluvial/lacustrine, feldspar-rich quartz sandstone, deep red in color with white mottling. Only the top few feet of the formation rise above lake level within the Lakeshore (e.g., vicinity of Au Sable Point). This formation was quarried on nearby Grand Island for building stone in the late 19th century. The western side of Grand Island, within the Hiawatha National Forest, features spectacular Jacobsville cliffs.

The Mid to Late Cambrian, light grey to white Munising Formation lies unconformably above the Jacobsville. The Munising Formation probably represents a complex shoreline/shallow water environment that was influenced by fluvial, wave, tidal and aeolian processes. The Munising is divided into three members: the basal conglomerate, the hard Chapel Rock sandstone, characterized by large, sweeping cross beds and the crumbly Miners Castle sandstone.

Capping the easily eroded Miners Castle Member of the Munising Formation in the western half of the Pictured Rocks, is the resistant Early Ordovician Au Train Formation. The Au Train Formation is a light brown to white dolomitic sandstone that lies above the distinctive caprock above the lip of Munising and Bridalveil Falls.

Fossils are completely absent from the Jacobsville Formation and uncommon in the Munising Formation. Fragments of trilobites have been found in the Miners Castle member and 26 taxa of conodonts in the upper Munising Formation and the lower Au Train Formation. The Au Train also contains Middle Ordovician cephalopod and gastropod fossils.

Structurally, Pictured Rocks National Lakeshore lies along the northern edge of the Michigan Basin, thus sedimentary bedding dips gently toward the south. Strata also rise very slightly eastward in the vicinity of the Lakeshore so that the Jacobsville, which is below lake level at Miners Castle, is well exposed to the east of Hurricane River Campground, at Au Sable Point, and in the gorge at Sable Falls.

Glaciers / Glacial Features

During the Pleistocene epoch, ice sheets of all four North American glacial stages advanced and retreated through the area. The Valders advance, one of the last substages of the Wisconsinan glacial period, wiped the surface clean and left only its record about 12,000 years ago. A brief re-advance of ice, the Marquette substage, occurred 10,000 years ago in northern Upper Michigan.

Melting of glacial ice within the Superior Basin produced huge rivers that deposited millions of tons of pulverized rock rubble in various configurations to the south of the Superior basin. A sheet of outwash, of varying thickness, was deposited along the south edge of Pictured Rocks National Lakeshore between Wetmore and Seney by southward flowing "braided" glacial streams. The material underlying the present-day Kingston Plains was deposited in this way. Kingston and Nevins lakes are examples of "kettle hole lakes" within the outwash. The Grand Sable Banks near Grand Marais perhaps originated as a glaciofluvial crevasse filling or kame terrace.

Meltwater carved several channels into Cambrian sandstone bedrock; the most prominent of these are now occupied by Chapel Creek and Mosquito River and by Beaver Basin. As ice retreated completely from the Superior Basin, water levels in the basin receded rapidly northward leaving the Pictured Rocks area "high and dry" about 9500 years ago. This occurred as outlet channels to the east remained at low levels due to the recent loading of glacier ice.

Between 6,000 and 4,000 years before present, "isostatic rebound" of the earth's crust from its "depressed" state began to accelerate as land was relieved of the huge weight of the ice sheets. The rise of the outlet of ancestral Lake Superior (at North Bay, Ontario) caused lake level to rise relatively quickly to a level roughly 13 m (40 feet) higher than present Lake Superior. This high lake stand has been designated Glacial Lake Nipissing. Slowing of rebound, downcutting of channels through unconsolidated material, shifting of outlets to the south and climatic change subsequently caused a lowering of Lake Superior to near its present level.

As lake levels rose about 5,000 years before present, the Grand Sable Banks were destabilized and part of the glaciofluvial deposit was reworked by wind to form the Grand Sable Dunes. During the Nipissing "high stand," Chapel Rock and Miners Castle as well as many less prominent features were carved into the Cambrian sandstone by wave action. Beaver, Trappers, Little Beaver, Chapel, Little Chapel, and Miners Lakes represent embayments on ancient Lake Nipissing.

As erosion lowered the Lake Nipissing outlet to the modern Lake Superior level during a 1,600 year period, lake currents deposited a succession of parallel beach ridges from the Nipissing level to the present beach. These closely spaced ridges which form a "corrugated plain", are evident in the vicinity of Au Sable Point, along the trail from Little Beaver Lake Campground to Lake Superior, on Sand Point and on the tombolo between Trout and Murrays Bay on Grand Island.