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A Glacial Winter

Imagine the worst winter day you have ever experienced in Anaconda. It is probably not a pleasant memory - wind blasted snow, roads covered in snow or closed; some may even remember having to travel on foot, snowshoes or even horse back.

Looking back 20,000 years to the peak, or glacial maxum, of the latest glacial event, Mount Haggin is barely visible behind mountain glaciers. What is now Anaconda's west valley were rivers of ice carving U-shaped valleys and bulldozing car sized boulders and debris ahead and along canyon walls. Below the glaciers were torrents of melt-water and debris covering the valley floor with gravel and enormous boulders. Haggin Lake is likely a tarn (a small mountain lake resulting from glaciation) carved out by the head of a mountain glacier.

Landmarks are meaningful to communities and travelers. A brightly painted yellow rock west of Anaconda in Warm Springs Creek is a well-known but maybe poorly understood relic of the glacial period. It could have originated from the Anaconda Range and dropped there when the glacier melted (called an Erratic) or, and more likely, it was washed down in glacial meltwater or floating in a larger chuck of ice which later melted. Some may think it nothing but a notable curiosity while others find it convenient to assess stream flow since it is painted only to the water level that existed at the time.

Traveling along trails on the south side of Garrity Mountain,, piles of boulders are an indication of the extent of a glacier. These boulders have been bulldozed ahead or alongside a glacier and left as a rubble pile as the glacier melted. All along the south Mount Haggin valley trail are continuous examples of boulders and other debris left along the margins (lateral moraine) and the toe (front or terminal moraine) of a glacier. Look closely through the trees for ridges of boulders overgrown with shrubs and trees.

Further up Warm Springs Creek on the north side of Highway 1 is a hummocky terrain. These slight hills or mounds are not erosional features left by streams of spring melt water, but are remnants of the sand and rocks frozen in the glacial ice and dropped upon glacial melting. (W.C. Alden, "Physiography and Glacial Geology of Southwest Montana",1953, USGS Prof. Paper 231). Alden also reported that the glaciers of the Anaconda Range extended to within 7 miles of Anaconda.

Keep your eyes open for some interesting features in the thick timber on the south valley of Garrity Mountain. These appear as small ponds, some with water or evidence of water. There is neither a spring feeding them nor an outlet draining them. These depressions formed when a large block of ice broke free from the base of the receding glacier. Ice, and the debris it contained, was covered with gravel and sand from the melting glacier above. Later this large block of ice melted and left a depression or Kettle. I wouldn’t suggest drinking the water nor fighting the mosquitoes to get near it.

More landmarks next time.

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