Alpine glaciers of the Smiths Fork (Pinedale equivalent) and Blacks
Fork (Bull Lake) glaciations on the north slope of the Uinta Mountains
were strongly controlled by local structural geology. Hogbacks of resistant
Paleozoic limestone flank the mountain range and intersect all major glaciated
valleys of the north slope. Larger glaciers west of the range center
effectively removed this barrier and flowed unimpeded northward to the
Wyoming-Utah border. Glaciers east of the range center were restricted
by the limestone ridge, and were correspondingly limited in their northward
This relationship has implications for the distribution of glacial deposits and for paleoclimate inferences made from mapped glacier extents. In valleys where the Paleozoic unit forms a prominent restriction, Smiths Fork and Blacks Fork-age glaciers were of more or less identical size. This situation is well displayed in the valleys of Burnt Fork and Henrys Fork. In Burnt Fork, the Smiths Fork-age glacier terminated against the upstream side of the limestone hogback that rises 170 m above the valley floor. No unequivocal glacial deposits are found beyond the hogback suggesting that the ridge formed a barrier to ice flow in all preceding glaciations. In Henrys Fork, the most recent glacier advanced several km beyond the hogback. However, widespread stagnant ice terrain extending northward from the limestone ridge to the terminal moraine indicates that downwasting of the ice surface at the onset of deglaciation resulted in decoupling of the ice north of the hogback as the main valley glacier retreated southward.
Glaciers in western valleys, where the hogback had been removed by glacial erosion, retreated actively with numerous pauses represented by recessional moraines. Recessional moraines are particularly common along the Blacks Fork and branches of the Bear River. This observation suggests that the mass balance of glaciers of the eastern north slope may have allowed them to advance further north if their valleys had not been restricted by the limestone outcrop. Eastern glaciers may have remained at their terminal positions longer than those further west.
Uinta-Mountains, Pinedale, Alpine-Glaciers