126 GEOLOGICAL HISTORY OF LAKE LABONTAX. 



The illustrations of sections accompanying the following pages were 

 drawn by Mr. W J McGee, to whom I am also indebted for a number of 

 the observations liere included. 



EXPOSURES liS' THE CANO^T OF TUE HUMBOLDT. 



Between Golconda and Humboldt Lake the Humboldt River flows in 

 a channel that it has excavated in Lahontan sediments since the last desicca- 

 tion of the ancient lake. For a number of miles below Golconda the river 

 is practically a surface stream, with low banks of marly clay belonging to 

 the upper lacustral series. At Mill City its channel commences to deepen, 

 and at Rye Patch the river flows a little moi'e than two hundred feet below 

 the general level of the desert. The general appearance of the gorge exca- 

 vated by the river through the plain formed of lacustral sediments is shown 

 in the accompanying illustration, Plate XXII, which is a reproduction of a 

 photograph taken on the brink of the canon, opposite Rye Patch. Through- 

 out this portion of the caiion the tripartite division of the strata exposed in 

 the steep banks is easily distinguished where not obscured by debris slopes. 

 Below Rye Patch the banks decrease in altitude, and south of Oreana they 

 are seldom more than 40 or 50 feet high, and only exhibit sections of the 

 upper lacustral clays, with traces here and tliere of the medial gravels. 



A section of the beds exposed in the sides of the Humboldt Canon be- 

 tween Mill City and Lovelock Station, a distance of over 50 miles, is rep- 

 resented at the top of Plate XXIII. This section was compiled from about 

 25 detailed sections, which were first drawn at their proper place on the 

 general diagram and then united in the manner that a somewhat extended 

 study of the exposures seemed to dictate.^^ A few local sections, drawn with- 

 the same vertical and horizontal scale, are represented in the lower portion 

 of the plate, and illustrate the diversity that prevails throughout the expos- 

 ures. The most striking feature in the general section is the thickening 

 of the deposits near Rye Patch, where they form an arch that once com- 

 pletely dammed the valley and was subsequently dissected by the river. 

 The hypothesis framed by the writer in explanation of the phenomena ob- 



■" This illnstratiou is perhaps open to the criticism that too luiich promiucnce has been given tO' 

 tho apparent jilication of the strata. 



