Geology question

Question

5. You notice the following in a stream-cut gorge. In the lower part of the gorge you see a bedrock surface with linear scratches and polish that is overlain by a 12 meter think layer of poorly sorted mud, sand, and gravel with some gravel up to 2 meters in diameter. Next upward are moderately well-sorted layers of cross-bedded sand and horizontal layers of conglomerate. Decipher the geologic history revealed in these two rock layers. 

Answer 1

The bedrock in the lower part of the gorge has been eroded by ice and rocks during a period of glaciation, resulting in the striations and polished areas. When the climate warmed up and the glaciers melted, rapidly flowing streams carrying runoff carried and deposited the 12 m thick layer of poorly sorted debris. This depositional period was followed by slower flowing streams depositing bed load sand in cross bedded migrating dunes / bars and then finally by slower moving bed load sand being deposited in horizontal layers.