Cretaceous rocks along part of southeast boundary of Glacier National Park, Montana
Cobban WA. 1956. Cretaceous rocks along part of southeast boundary of Glacier National Park, Montana. Bulletin of the American Association of Petroleum Geologists. 40(5):1001-1004
Although the presence of Cretaceous rocks along the east margin of GLAC has been known since 1902, very little has been published about them. The few outcrops mentioned in the literature are identified usually as Kootenai, Benton, Colorado, or undifferentiated Cretaceous. These rocks are intensely disturbed inasmuch as they lie below or near the Lewis overthrust fault (Precambrian over Cretaceous). The Colorado shale forms most of the outcrops along U.S. Highway 2 between East Glacier and the Continental Divide (Marias Pass) at Summit. The writer has shown that the rocks on the Sweetgrass arch lying east and southeast of GLAC, the Colorado shale, are divisible into many persistent lithologic units which can be correlated with named units elsewhere. Reconnaissance work along the southeast margin of GLAC reveals the presence of some of these subdivisions. The purpose of this report is to draw attention to the better identified outcrops along U.S. Highway 2 between East Glacier and Summit. Geologists visiting or working in the area may find the dated and identified outcrops of value in interpreting the complex structure and in lithofacies studies. The mileage readings begin at the bridge over Midvale Creek at the south edge of East Glacier. Where fossils are mentioned, references are given for good illustrations.