430 STEPHEN Ri CAPES) 
preglacial streams. Both passes were scoured deeply by glacial 
erosion, and when the ice retreated the low gaps were left. We do 
not know whether the early postglacial drainage followed the present 
lines or not, but as the valleys were gradually filled with glacial 
outwash gravels the streams flowed sometimes in one direction, 
sometimes in the other. Gulkana Glacier, in the fall of 1910, was 
observed to send most of its water into the Delta River drainage, 
although a small stream flowed to the Gulkana. The constant 
shifting of channels which takes place doubtless gives the Gulkana 
the greater portion of water in some years. 
COPPER RIVER BASIN 
Between Delta and Mentasta passes there is a large number of 
glaciers draining by various tributary streams into Copper River. 
As the mountains are here all less than 10,000 feet in elevation, 
the glaciers are in general smaller than those of the higher moun- 
tains west of the Delta. Mendenhall, who visited these glaciers 
in 1902, says" 
The most conspicuous of them is the one in which Gakona River rises 
(Fig. 7). It is perhaps 12 miles long and expands near its foot to a width of 
3 miles. This lower portion is a rough, pinnacled mass of ice which rises several 
hundred feet above the valley floor on either side, and is visible for many miles 
in either direction. 
Chistochina Glacier fills the greater part of the narrow piedmont valley 
north of Slate Creek and the upper Chisna. It flows east and west into 
branches of Chistochina River, and recelves as tributaries a number of smaller 
glaciers which flow down from the crest of the range. 
Mendenhall fails to state whether the glaciers at the time of 
his visit gave evidence of recent retreat or advance. 
GLACIO-FLUVIAL DEPOSITS AND MORAINES 
Great areas in the Copper River basin are covered with deposits 
which are directly or indirectly of glacial origin. In the inter- 
stream areas these beds are composed largely of glacial till. Along 
the stream courses there are extensive deposits of glacial outwash . 
_ gravels. Their distribution is shown on Plate I. 
«W. C. Mendenhall, “Geology of the Central Copper River Region, Alaska,” 
Prof. Paper U.S. Geol. Survey No. 41, 1905, p. 89. 
