14 THE PORCUPINE PLACER DISTRICT, ALASKA. [bull. 236. 
TOPOGRAPHY. 
MOUNTAINS. 
The mountains of the Porcupine district are an eastern wing- of the 
lofty St. Elias Range. Viewing the region from one of the summits 
the general aspect is that of a high plateau dissected by numerous deep 
and narrow valleys. The surrounding peaks are rugged and precipi- 
tous, from 5,000 to 7,500 feet in elevation, below which glaciers and 
fields of snow fill the uppermost parts of the valleys and canyons. 
The mountain slopes, which rise gradually, with no abrupt benches 
or terraces, have all been rounded by moving ice, and there is evi- 
dence to show that all but the highest peaks were once buried beneath 
a continuous field of ice and snow. 
DRAINAGE. 
Of the many rivers entering Lynn Canal the Chilkat is the largest, 
draining, with it tributaries, the country within 60 miles of its mouth at 
Chilkat Inlet. Most of its waters come from melting glaciers and snow 
fields. Near its head it runs through a canyon-like valley extending 
down to the mouth of Bear Creek, a western tributary, but from this 
point flows in many channels over a broad gravel flat. It has built a 
delta 2 miles wide at its mouth and is slowly filling up the head of the 
inlet. The eastern slope of its lower basin is very abrupt and is char- 
acterized by rounded peaks of intrusive rocks, averaging' 5,500 feet in 
elevation, while to the west the bank rises to a densely wooded ridge 
of 1,500 feet elevation, composed mainly of slate, back of which are 
high, snow-covered mountains. 
The most important tributaries of Chilkat River are the Klehini, 
the Salmon (Tsirku), and the Takhin, named in order of size. The first 
named is a rapid river, averaging 100 feet in width and rarely exceed- 
ing 5 feet in depth. Eighteen miles from its mouth it, like the Chilkat, 
changes from a gravel filled valley a quarter of a mile or more in 
width to a comparative^ narrow, steep-sided canyon. Its waters are 
seldom confined to one stream, but are divided by many gravel bars 
into a network of interlacing channels. Its main channel is continu- 
ally shifting, rendering canoeing or sailing up the river difficult 
to the inexperienced navigator. Many of the smaller streams, flow- 
ing at right angles to the river, are glacier-fed mountain torrents, 
too steep and rapid for canoes, and often impossible to ford during 
high water, even near their sources. 
At the mouth of Porcupine Creek is a gravel deposit extending 1 
mile to the westward and lying from 60 to 80 feet above the river bed; 
this deposit probably represents a former delta of the creek, having 
been built up when the river was at that height. On this terrace the 
town of Porcupine has been built. 
