Mount Shasta was sculpted by glaciers during the Pleistocene but Recent volcanic activity has covered up many of the glaciated landforms. What does remain from the Pleistocene are the moraines from Mount Shasta that extend into the Shasta Valley to the northwest (which shows how much larger the Pleistocene glaciers were) and the glacial features on the south side of Mount Shasta around the Old Ski Bowl. All of the glaciers that currently exist on Mount Shasta are neoglacial, formed after the Ice Ages, and will be discussed later.
Glaciofluvial deposits encircle Mount Shasta like a donut, with the ring of debris about 10 miles from the summit of Mount Shasta (and even further out on the north side of the mountain). These deposits, at least on the northwest side of Mount Shasta, are from the Pleistocene as lava flows from the early Holocene pour over the glacial deposits. There are also Holocene glacial deposits overlying the older Pleistocene deposits, especially in the Whitney-Bolam debris fan which stretches clear to Lake Shastina. Besides the outwash fan which stretches to Lake Shastina and covers most of Juniper Flat, you can see glacial deposits at the I-5 roadcut just north of Weed.
Sargents Ridge is the oldest cone on Mount Shasta. Sargents Ridge has been affected by both the Tahoe and Tioga glaciations as evidenced by old till deposits (Christiansen, 1976). Misery Hill Cone was affected by Tioga glaciation but was not formed until after the Tahoe Glaciation (Christiansen, 1976; Hill, 1984).
On the south side of the mountain to the east of Avalanche Gulch, but still on the west side of Sargents Ridge, are several cirques: Sun Bowl, Powder Bowl, and the Old Ski Bowl (Selters and Zanger, 1995). Also on the south side of the mountain to the east of Panther Creek is Gray Butte. The 8,108 foot peak of this plug dome appears to be a horn with a col on its northern arête, and two subsidiary peaks on the south and east arêtes. The cirque on the west side of Gray Butte is the source of a tributary of Panther Creek. The well-developed cirque on the east (in bottom right portion of below image) is the source of a spring and stream which flows into Panther Creek on the south side of McKenzie Butte. The less-developed southern cirque has a switch-back leading up to the radio tower.
Northwest of the bowls is Avalanche Gulch, a glaciated valley on the southwest side of Mount Shasta. Casaval Ridge separates Avalanche Gulch and Cascade Gulch, which is to the northwest of Avalanche Gulch. On the west side of Casaval Ridge, in Cascade Gulch, is a series of cirque basins, Hidden Valley being one of them. The cirques don't show up very well on the topo map, but they are clearly illustrated in the 1883 map showing the glaciers of Mount Shasta. Presumably, the areas just described were glaciated at the end of the Pleistocene through the beginning of the Holocene, but I'm not sure.
Cirques on the Northwest Side of Casaval Ridge
(Casaval Ridge extends from the center of the photo to the bottom left corner.)
Segment of Plate XLIV of the 1883 Fifth Annual Report