sheet and advanced south into the Skagit River drainage. Skagit ice passed through Fisher and Rainy passes, and down Bridge Creek into the Lake Chelan valley. The glacial lobe flowed down the Lake Chelan valley until meeting glacial ice of the main Okanogan Lobe advancing up the valley from the Columbia River drainage near Manson, Washington. The deposits of the northwestward advancing Okanagan lobe are characterized by large, basalt glacial erratics. As the Skagit Lobe during the Last Glacial Maximum and glacial lobes during older glaciations flowed to the southeast down the Lake Chelan valley, they excavated the deep glacial trough that is now occupied by Lake Chelan. The depth of the Lucerne Basin and the elevation of glacial till and moraines and glacier-scoured bedrock on the walls of the overdeepened Lake Chelan valley indicates that the thickness of the Skagit Lobe was over . Basins Lake Chelan is composed of two basins. The lower basin, Wapato, is shallower and approximately a fourth the total length of the lake. The upper basin, Lucerne, is much deeper and extends for the remainder of the length of the lake. The two basins are separated by a sill rising to within of the surface, at a point known as the narrows, at which the lake is only wide. The lower basin, Wapato, is the shallower of the two, with a maximum depth of only . About of glacial sediment and rockslide deposits rest between the lake bottom and bedrock. This section of the lake is long, and has an average depth of . Due to the relatively modest size of this basin, water resides in this basin for only 0.8 years, compared to 10 for Lucerne Basin. The upper Lucerne basin is long with an average depth of and thus by far the larger of the two basins. It is in this part of the lake that the maximum depth of is found. Lucerne basin contains 92% of the water in Lake Chelan and 74% of the surface area, leaving Wapato with only 8% of the total volume of water and 26% of the surface area. The upper basin of Lake Chelan is surrounded by more mountainous terrain, resulting in few beaches along the shoreline. Approximately of the shoreline of this basin are in National Forest lands, and in National Park lands. Natural history Climate The climate of Lake Chelan's watershed is varied.