584 J. H. BRETZ GLACIAL DRAINAGE OX COLUMBIA PLATEAU 



Creek and in the larger valley are great l)ars and terraces of coarse 

 basaltic gravel, poorly sorted and much of it siibangular. ]\[ingled with 

 it are a few cobbles and small boulders of granite and quartzite. The 

 material farther down Pine Creek Valley is finer and better sorted. It 

 seems clear that most of the debris was derived by erosion of the spill- 

 ways themselves, only a small amount of foreign material crossing the 

 lake on ice-rafts from the front of the ice-sheet. 



The valley during this episode in its history was hut a cliannel. The 

 glacial stream filled it from side to side for a depth of tens of feet. This 

 is shown a few miles above Maiden, where the stream flooded over a low 

 shoulder of l^asalt, cutting a channel in the rock at least 40 feet deep, 

 though the main valley alongside was wide open and received gravel 

 deposits. Xorth Pine Creek now flows through this channel. The main 

 current of the stream here cut across a curve in the preexisting valley. 

 The gradient of this glacial stream was close to 30 feet to the mile in its 

 upper part and a])out 20 feet to the mile in the lower part. 



The character of the terraces in Pine Creek Valley below the junction 

 of North Pine Creek is instructive. Like the Pantops deposit, tliere are 

 no well defined depositional forms. The terrace tops do not abut sharply 

 against the hillslopes, but instead waste has crept out on the gravel de- 

 posits from the slopes above, and the valleyward edges of tlie terraces 

 liave l)ecome rounded and notched by widened gullie- until tlie terrac;' 

 form is obscure. This is well shown at Kenova, where tlie Chicago, Mil- 

 waukee and Saint Paul Eailroad has opened a large pit in the gravel. 

 Furthermore, these terraces are only fragments here and there of Avhat 

 was once a continuous filling. Despite these evidences of considerable 

 age, the material in the deposits appears fresh. It is unstained and 

 uncemented. 



Only one other glacial drainage route across the mature Palouse coun- 

 try is known, and this was but a tributary to the Pine Creek channel. 

 Waters from glacial ice spilled southward through a low ])lac? at ^lica 

 i)etween Moran Peak on the west and Mica Peak on the east. The alti- 

 tude of the col at Mica is hardly 10 feet above that southeast of S])angle. 

 Ponded waters of the Latah Valley mu>t have backed up almost t;) the 

 village of Mica. Whether or not a considerable lake lay to the north of 

 the Mica col,^ it is certain that the ice-sheet was hard against tli- north- 

 ern flank of Moran Peak and its drainage probably })asse(l through a 

 settling basin before entering the short Mica channel. A few erratic^-, 

 one of them striated, have been found in the channel, but no glacial 



'Lake Spokane" of Large. 



