GLACIERS OF THE SIERRA COSTA MOUNTAINS 49 
altitude, its heavy ground moraine, and its beautiful terminal 
moraine. 
At its maximum extension, this glacier had a length of not 
less than fifteen miles, a width of one half to one mile, and a 
depth of 1000 to 1500 feet. It was the largest single mass of 
ice, so far as I know, of the Sierra Costa Mountains. It headed 
among the peaks in the highest portion of this range, at an alti- 
tude now about 6500 feet, trended in an easterly direction, 
forming the broad flat of the Mumford meadows (altitude 5500 
feet), then ran southeasterly, descending rapidly to a level now 
little more than 3500 feet above the sea, where at ten miles 
from its head, it suddenly issued from the high mountains, and 
turning to the northeast, it deployed upon and across a broad 
basin valley of Miocene age and later, and terminated very close 
to the site of the Redding and Trinity Centre road at an eleva- 
tion now no greater than 2500 feet above the sea. Here are, 
so far as I am aware, the least elevated direct glacial deposits 
west of the Sacramento River, if not in the whole state of 
California. 
Among the prospectors of northern California, the “‘cemented 
gravel of Swift Creek” is a term to conjure with. It is essen- 
tially non-gold-bearing, and so far as the ability of the average 
miner to sink a shaft through it is concerned, it is bottomless. 
It is an unstratified agglomeration of bowlders, cobbles, pebbles, 
sand, silt, and clay, which occupies the valley from head to 
mouth, forms the flats or meadows, and is trenched by a narrow 
canyon carved by Swift Creek in postglacial time. Where the 
stream, in undermining a bank, has made a recent excavation, 
the deposit has an extremely fresh appearance and a delicate 
light bluish tint. Many of the included bowlders are rounded 
and polished, and not a few are beautifully striated. It is as 
typical a till as any tobe found on this continent. Being largely 
the result of glacial abrasion on the rock floor and walls of the 
valley (serpentine mainly), it is slightly cemented by the large 
constituent of unoxidized magnesian and calcareous salts. Most 
of the included rock fragments are serpentine of the black 
