EMBANKMENTS AT HUMBOLDT LAKE. 107 



bars with rounded crests, thus securing the highest records of wave action 

 in this portion of the former lake. One result of these measurements is the 

 proof that the beach lines on the sides of the valley, although formed at the 

 highest water stage of the former lake, and therefore originally in the same 

 horizontal plane, no longer have the same elevation. On the east side, the 

 highest water line is now 498 feet above the level of Humboldt Lake, while 

 on the west its elevation is 489 feet. Humboldt Lake, as shown by con- 

 necting our line of levels with the profile of the Central Pacific Kailroad, is 

 3,929 feet above the sea. 



In studying these wave-built structures more minutely, we find that 

 the one which crosses the valley is composed of worn and rounded pebbles 

 of basalt, rhyolite, granite, and quartzite, together with fragments of black 

 slate and occasional masses of cemented pebbles. The granite and quartzite 

 and the volcanic rock forming some of the pebbles are only found in place 

 in the vicinity on the north side of Humboldt Lake; consequently, the 

 currents which carried them to their present positions must have come from 

 the northeast and followed the western border of the valle}' until deflected 

 by the topography of the coast. The direction of the currents th.it built 

 this embankment is also indicated by its form: to the westward it presents 

 a steep escarpment, but the eastern slope is quite gentle and, especially 

 near i.ts extremities, merges gradually with the alluvial slopes in the sides 

 of the valley. The more gentle slope indicates the general direction from 

 which the current-borne debris was derived. In the following section a 

 profile of the bar is given, constructed with the same vertical and horizontal 

 scale, from a line of levels run at right angles to the trend of the structure 

 at a point about two miles west of the gap cut by the overflow of Humboldt 

 Lake. 



!N Leva/ of_ ■ Humbq/r^ f Ls^ k^ 1' 



Fig. 16. — Profile of gravel cDibankment at west end of HnniboUlt L.nlie. 



The topography of the embankment, therefore, as well as the material 

 of which it is composed, indicates that it was built very largely by currents 

 from the north. It is highest at the northern end, near wliere the railroad 



