46 STEPHEN R. CAP PS 



All of the larger tributaries of the Chisana River, including Bow, 

 Gehoenda, Chathenda, and Chavolda creeks from the east and 

 Cross Creek from the west, have valleys floored with gravels, and 

 most of these streams have developed fans where their gravel bars 

 coalesce with those of the main valley. 



Terraces. — Conspicuous terrace deposits occur at several points 

 along the valleys of the Chisana and its tributaries. East of Euchre 

 Mountain, and including the lower portions of Bow, Gehoenda, and 

 Chathenda creek valleys, there is a broad area of gravel deposits 

 into which these streams have entrenched themselves. The area now 

 covered by these gravels was formerly occupied by the Chisana 

 Glacier. As the glacier decreased in size the ice-edge gradually 

 shrank back toward the west and exposed this region, while it was 

 still of sufficient thickness in the main Chisana Valley to form an 

 obstruction to the streams from the east. Under these conditions 

 the creeks rapidly built up their valleys with alluvial material. It 

 is even possible that temporary lakes were formed behind the ice- 

 dam. An exposure along Gehoenda Creek for several miles above 

 its mouth shows fine, stratified gravels and silts, interbedded with 

 coarser materials. The rather perfect stratification of the finer 

 materials suggests a lacustrine origin for these beds. 



On Notch Creek there are terrace gravels on both sides of the 

 stream. They occur intermittently from the base of the mountains 

 near the head of the creek to its mouth, and in places the stream-cut 

 bluff shows a section of 150 feet of the coarse, rudely stratified gravels 

 with interbedded lenses of sand. They are evidently stream-laid 

 and may have been deposited synchronously with the terraces in the 

 Nabesna Valley described above. 



About ten miles below the mouth of Chavolda Creek, on the 

 northwest side of the Chisana River, there is a good exposure of 

 terrace gravels. In the bank about 60 feet high the lower 40 feet 

 are exposed. The section (Fig. 6) shows 15 feet of coarse gravel at 

 the base, with occasional bowlders 18 inches in diameter. Above 

 this is 25 feet of fine, well-stratified gravel with pebbles five inches or 

 less in diameter. The terraces were probably built contempora- 

 neously with those in Notch Creek. 



Extent of earlier glaciers. — ^As is the case in other valleys of this 



