For the last ten years, during which the survey of the San Juan region of Colorado has been in progress, evidence has been accumulating showing that in all probability the mountains have been subject to more than one period of glaciation during Pleistocene time. The fact of more than one stage of glaciation in the Rocky Mountain region was established by Salisbury and Blackwelder† in 1902 through observations made in the Bighorn mountains, Wyoming. More recently, Capps and Leffingwell* have drawn similar conclusions from studies in the Arkansas valley, in Colorado.
Evidence of the last stage of glaciation is obvious in the San Juan mountains, and abundant proofs have been found throughout the region examined that the ice disappeared in relatively recent times.† What may be traces of an earlier stage have been observed at a number of localities, but until lately satisfactory evidence in this connection . . .