NO. 4 A FOLSOM COMPLEX ROBERTS 1 3 



the present overburden when sand, gravel, and boulders were swept 

 down into the valley from its, bordering hills. Later, water, coursing 

 its way down the hillsides and along the valley, cut the gully in whose 

 banks the midden deposit was revealed. 



The present ravine is only one of several channels which have from 

 time to time been worn in that portion of the terrain. Traces of other 

 water courses which did not cut so deeply into the valley fill are 

 apparent in the sides of the gully. One old channel passed directly 

 over the top of a portion of the layer in which most of the stone and 

 bone material was found. It did not wear its way down into the old 

 soil line but stopped a few inches above it and then began to build up. 

 It gradually became filled, until, so far as surface indications are con- 

 cerned, it was completely obliterated. The direction of the old channel 

 at this point had been almost at right angles to the now existing gully. 

 In character the former suggests a meandering stream, one which 

 probably continued to the lower end of the valley a mile or so east of 

 the mouth of the channel of today. The filling of the stream bed may 

 have resulted from damming by alluvial gravels washed in from one 

 of the side canyons near its mouth. Considerable time is probably 

 represented by all this action, although conditions in the West are 

 such that channel cutting, filling, and shifting may occur in a relatively 

 short period of years. Other factors indicate that the process here 

 could not have been extremely rapid because ridges from which some 

 of the valley fill was eroded have since completely disappeared, having 

 been weathered away in the opposite direction. This is shown by the 

 fact that the soil layer — ^the artifact-bearing stratum — topping the clay 

 bed is still on the upslope, where it appears along the edge of the 

 terrace above the broad valley to the south of the site. The complete 

 erosion of the ridge transformed the level from a valley bottom to 

 what may possibly be considered to be a terrace. 



One aspect of the problem which is of interest, although it bears 

 only indirectly on the archeological factor, concerns the original scour- 

 ing of the valley bottom and removal of material down to the Oligo- 

 cene stratum. Whether this resulted from action by mountain glaciers, 

 by water from them, or from some more recent agent is one of the 

 many phases of . the subject which geologic studies may explain. 

 Should it be established that the Oligocene deposit was laid bare at the 

 time of the great mountain glaciers, which are considered to have been 

 contemporaneous with the Wisconsin ice sheet, a significant inference 

 could be drawn, namely, that makers of the implements arrived on the 

 scene not long after the retreat of the ice. since evidence of their 



