SECTIONS EXPOSED IN WALKER OAJfON. 139 



structure of the Lahontan sediments exposed in the canon walls for a dis- 

 tance of 18 miles. The highest point in the section is at the crest of the 

 embankment, which crosses the valley and marks approximately the level 

 of the highest water stage of the former lake. Between the embankment 

 mentioned above and Walker Lake, a distance of 8 miles, the river banks 

 vary from zero at the lake to 50 or 60 feet in the neighborhood of the em- 

 bankment. In this interval the exposures are almost entirely of upper 

 laeustral clays, with intercalated beds of volcanic dust, but at a few locali- 

 ties, in the nortliern portion of the section, the medial gravels and under- 

 lying clays may be seen at the base of the escarpment bordering the river. 

 Where the stream-channel crosses the embankment, the entire exposure, 200 

 feet high, is composed of inclined and arched strata of sand and gravel 

 inclosing irregular and loamy beds. The entire series has a characteiistic 

 pinkish tint due to the presence of iron oxide. This embankment occurs 

 unconformably between the upper and lower clays, and, like many similar 

 structures when seen in section, exhibits anticlinals of deposition. Its base 

 is not exposed to view, but as the clays of the lower series occur near at 

 hand, both to the north and south, it seems probable that the gravels com- 

 posing the embankment were, at least in part, accumulated during the time 

 the lower clays were being deposited. Like the embankment at the south- 

 ern end of Humboldt Lake, this structure was pi'obably begun early in the 

 history of Lake Lahontan, and has been enlarged many times since. The 

 last addition was contemporaneous with the deposition of the upper clays, 

 or perhaps in part subsequent to it; in the main, however, it is composed 

 of the medial gravels of the Lahontan series. Northward from the crest 

 of the embankment the canon walls decrease in height, as represented in 

 Fig. C, Plate XXVIII, all the way to Mason Valley, where the river becomes 

 a surface stream. The medial gravels are exposed for about 8 miles north 

 of the embankment, and appear again at a point where they have suffered 

 some local disturbance about 4 miles below tiie point where the river 

 leaves Mason Valley. 



Throughout the entire exposure of lower laeustral clays observed in 

 the Walker River Canon, the strata are of light-colored, laminated, marly 

 clays, of the same nature as the corresponding beds occurring in the Hum- 



