GLACIERS OF THE SIERRA COSTA MOUNTAINS SI 
and even crests, trend from the sides of the mouth of the upper 
valley northeastwardly across the Miocene basin, gradually 
descending toward Trinity River. Between them is a flat- 
bottomed, steep sided depressed area, 300 to 500 feet in depth 
and one half mile in width, evidently representing the cross- 
section of the glacial tongue. From the crests of the ridges 
more gentle slopes of very bowldery land extend outward and 
gradually merge with the erosion surface. These ridges are the 
extra-montane extensions of the lateral moraine, but also con- 
tain ground moraine and may be considered a terminal moraine. 
Near the Trinity River they flatten down, become hummocky 
and indistinct, but appear to curve around the end of the site of 
the ancient glacier and connect, except for the postglacial 
canyon which the stream has cut thru the moraine. Beyond this 
is a fine example of a fan-shaped extra-glacial delta, which occu- . 
pies several square miles in the valley of the Trinity River, and 
its outer edge descends almost. to the level of that stream itself. 
This glacial tongue reached the northern end of the low 
Minerva range of mountains, and built its moraine across the 
mouths of several of the gulches. These have been filled nearly 
to the level of the moraine summit by fine silts, and form 
extensive grassy flats composed of deep black soil free from 
pebbles. Along the moraine the flats have some large angular 
erratics on their surface; these have slidden from the surface of 
the glacier. 
In the bottom of the depressed area within the moraine Swift 
Creek has eroded a canyon 75 to 150 feet deep and 300 to 500 
feet wide, widening and shallowing toward the mouth. This seems 
large, but represents glacial as well postglacial stream erosion. 
On the whole, the glacial features of the Swift Creek valley 
are extremely interesting and instructive, and, from its accessi- 
bility, should become classical among students of California 
Quaternary geology. 
The East Fork glacier—This occupied a high valley, steeply 
descending on the east face of Granite Peak, a few miles north- 
west of Minersville. Near its head a precipitous mountain side 
