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upon the baselevel of the Klamath Mountains, while in the opposite direction it appears to stretch up to the high plateau at the northern end of the Sierra Nevada, and shows the features already noted of tapering abruptly to the edge of the baselevel plain. This formation might be considered a fringe to the baselevel, and evidently was deposited at least in part during the baselevel period.

The earlier auriferous gravels upon the slopes of the Sierra Nevada are older than the volcanic flows of the same region. They are regarded by Messrs. Turner and Lindgren and the writer as of essentially the same age as the Ione formation in the Great valley of California. The auriferous gravels were accumulated and deposited upon the flanks of the range, while the finer material, sand and clay, were carried into the Sacramento valley.

The age of the baselevel must be determined by reference to the formation with which it is associated. It is evidently of more recent origin than the Cretaceous, since it truncates the upturned edges of the Shasta-Chico series, and these are the youngest strata upon which it has yet been seen. It was already developed at the time the earlier auriferous gravels were deposited, for they lie in the broad shallow valleys which belong to the baselevel plain. The erosion by which it was developed therefore occupied a part or the whole of the time interval between the upheaval of the land at the close of the Chico epoch (Cretaceous) and the deposition of the auriferous gravels.

The age of the earlier auriferous gravels has not yet been fully determined, although they have been the subject of much investigation. That of the later gravels will not be considered here. Professor J. D. Whitney, in his "Auriferous Gravels of the Sierra Nevada of California," page 283, says: "It appears probable, on stratigraphical grounds, that the detrital beds overlying the bed rock of the Sierra Nevada represent the whole