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The Upper Skagit Valley lies approximately 150 km east of Vancouver in the North Cascade Mountains. The Skagit River begins near Allison Pass in E.C. Manning Provincial Park and runs west to join the Sumallo River, almost doubling in volume where it now turns south and enters Skagit Valley Park. Just North of the Canada / USA boundary  the river flows into Ross Lake, a reservoir created by Ross Dam in Washington State. Skagit Valley Provincial Park borders E.C. Manning Provincial Park to the east and North Cascades National Park Service Complex to the south. These parks form part of a significant area of connected protected lands that span the international border.

The Upper Skagit Valley area is defined by SEEC as extending from Ross Dam in the south to the Skagit River headwaters to the north. This watershed area is a broad, U-shaped valley carved during the ice ages by advancing continental glaciers. Jagged peaks on surrounding mountains indicate where they protruded above the grinding ice that rounded off the lower mountains. The elevation where the jagged peaks begin indicates that the ice filling the Skagit Valley reached more than 1.5km thick.

This area is a transition zone between the wet, moderate climate found on the western slopes of the North Cascades and the dry, more extreme climate of their eastern slopes making the Upper Skagit a unique habitat for many species. The rain shadow effect of the mountains to the west limits the annual precipitation to about half that of nearby Hope, but the area still receives about twice the precipitation of the Okanagan Valley on the eastern edge of the mountains. Most precipitation usually falls during the winter, creating deep snowpack at higher elevations. Summers are typically dry and warm. Six bio-geo-climatic zones are represented here. The highest diversity of trees in all British Columbia is found here.

Ross Lake is a hydroelectric reservoir and the water level in the lake changes dramatically throughout the year because of both human management and the local climate. As precipitation on the mountains falls as snow during colder months, more water is released through the dam than flows into the reservoir and the water level in the lake drops. The lake usually reaches its lowest levels in mid to late April when snow stops accumulating and begins to melt. The amount of snowpack helps dam managers determine how low the water is drawn down. Winter “drawdown” may be as much as 30m (100 ft) or more below the full pool level. As spring weather warms and snow on the mountains melts more quickly, the water in the reservoir can rise 30-60cm (1-2 ft) per day. The reservoir is approximately 36km long when at full pool.

Skagit Environmental Endowment Commission, Geography, Upper Skagit WatershedSmall Glaciers

All the glaciers in the Upper Skagit Basin are temperate (warm) alpine glaciers. A temperate glacier is one where most of its ice is close to the melting point for the entire year. This constrasts with polar or “cold” glaciers that are well below the melting point all year. Most of these glaciers fall into one of two types.

Cirque Glaciers
Generally a small glacier occupying a cirque (a basin or amphitheater near a ridge crest). Most of these glaciers tend to be roughly circular with a width about equal to their length. Cirque glaciers average about 1 km2 and are usually less than 100 m thick. A significant number of the glaciers in the Upper Skagit River Basin are of this type.

Valley Glaciers
Long tongues of ice confined by valley walls. Unlike cirque glaciers, valley glaciers are significantly longer than they are wide and the altitudinal range of these glaciers is often large. Though uncommon in the Upper Skagit River Basin, valley glaciers such as Silver Creek Glacier are among the largest glaciers in area.

In the North Cascades region, the mass balance, stream flow, and the climate of South Cascade Glacier, the region’s benchmark glacier, are all monitored each year.

Glacier information and map image from “Glacier Change in the Upper Skagit River Basin”