An Archeological Survey of Development Projects Within Grand Portage National Monument, Cook County, Minnesota
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Chapter 2


This region of Minnesota is underlain by the Middle Precambrian Rove Formation. That formation is composed of easily eroded sedimentary rock (argillites and slates), as well as more resistant diabasic sills and dikes of gabbroic rock. These combine to form the remarkable surface relief of northeastern Minnesota through the effects of differential erosion. Both running water and glacial scouring have worked to create the rugged landscape that typifies this region (Grout and Schwartz 1933:94; Grout et al. 1959:134-135; Ojakangas and Matsch 1982:161-163, 175-176).

It is interesting to observe that the bedrock geology of the area can be considered the primary influence on the development of the fur trading concern at Grand Portage. Although the Pigeon River, which today forms part of the international boundary between the United States and Canada, was recognized as the best natural route to the northwestern interior, a series of highfalls and rapids makes its last 20 mi impassable by watercraft. Fortunately, the same geological conditions that produced those impediments also helped create a large embayment some eight miles south of the Pigeon River's mouth. Known today as Grand Portage Bay, that deep indentation into the Lake Superior coast line, which is further protected by Grand Portage Island, could provide safe haven for vessels transferring commodities of the fur trade. Furthermore, a small valley carved between stone dikes connected that bay with navigable waters of the Pigeon River. It was along that route that the portage was traced. Thus, it is the bedrock geology here that necessitated and enabled creation of the Grand Portage (cf. Woolworth and Woolworth 1982:1-3).

At this writing, no comprehensive soil survey data have been published for Cook County, Minnesota. Therefore, the soils about Grand Portage can be characterized only in the most general terms. Soils along the western shores of Lake Superior are, for the most part, post-Duluth glacial deposits representing former lakebeds and beach ridges. Consequently, they are composed largely of sand, with humic development in the upper reaches where vegetation has introduced organic materials. Gravels consisting of waterworn cobbles and pebbles are abundant throughout the soil column, especially in places where beaches were once active. That is most assuredly the case in the Grand Portage environs.


The climate of northeastern Minnesota is influenced not only by its northern latitude, but also by its proximity to the waters of Lake Superior. Temperatures here are usually cool, with an average annual mean of 4.5° C (40° F). According to current climatological data, the average daily mean temperature in January is -11.5° C (11° F), whereas the average daily mean for July is 15.5° C (60° F). The number of frost-free days per year varies from 80 to 140, which makes agriculture generally unreliable as a local subsistence strategy. Climatological records from 1988 indicate that snow typically falls in the northeast at the rate of 178 cm (70 in) a year. Winters are cold, and heavy snows can cover the ground for 100-140 days per year (Woolworth and Woolworth 1982:4).

Grand Portage lies well within what Dice (1943) terms the Canadian biotic province in his description and categorization of North American presettlement natural resources. Conditions vary widely through that biome, of course, depending on peculiar environmental factors. No doubt the influence of Lake Superior has a great effect on the plant and animal communities indigenous to the Grand Portage region. Furthermore, everywhere in North America current conditions are products of natural and cultural forces that have been constantly at work. As a result, it should not be surprising to find that many species present in the early Historic period can no longer be found in the area today.

The Canadian biotic province is typically characterized by heavy stands of trees, especially along inland lakes and streams. Hardwoods dominate, though they are mixed with a variety of subclimax species. In such lake forest environments, sugar maple is generally the most common tree species, followed by yellow birch, red pine, elm, aspen, basswood, hemlock, and white pine. Major subclimax species include black spruce, tamarack, and cedar, among others. At the present time, the dominant tree species about Grand Portage National Monument include a variety of conifers, birch, and aspen. Maple is present in significant numbers where microclimatic conditions are favorable, but hemlock is entirely absent from the Monument area.

Mammalian species supported by this environment include white-tailed deer, beaver, muskrat, snowshoe hare, and caribou. Many of these, of course, were important commodity resources of the fur trade. In addition, elk, moose, and black bear are present in the region. Many kinds of birds and waterfowl visit the area seasonally, including spruce grouse, raven, and loon. Of course, given the proximity of Lake Superior, a variety of fishes can be exploited, especially in the summer months when they are abundant.

Mason (1981:59-60) points out that the Canadian biotic province also supports a wide variety of plant resources that were utilized by prehistoric and historic Indian groups. In fact, he estimates that somewhere around 500 species were used for diverse purposes. Most were food sources, including those employed for beverages and flavoring. Other plants were collected for medicines and ritual consumption. Plants also served in the making of dyes and paints, as well as a host of other utilitarian items (e.g., baskets, canoes, cordage, etc.).

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Last Updated: 15-Jul-2009