RUSSELL.] LAKES. 33 
out leaving more than a faint trail. Their smooth surfaces are usually 
intersected in every direction by a network of shrinkage cracks, and 
about their borders there is in some instances a white incrustation of 
saline matter, which is left as the water which seeps down from the 
neighboring uplands is drawn to the surface by capillary attraction 
and evaporated. The characteristic vegetation about the borders of 
these and many other similar playas in the Great Basin region is the 
common greasewood. This shrub frequently attains a height of 4 to 
6 feet, and, like most desert plants, grows in isolated clumps. These 
bushes encroach on the playas, and occupy an advanced picket line, 
where the conditions leading to survival or death are nearly evenly 
balanced. One result of this delicate adjustment is that during the 
periods when the playas are desiccated the wind blows away the dried 
sediment from between the clumps of bushes, and also drifts fine 
debris about them, so that rudely circular mounds are formed, which 
in many instances are 8 or 10 feet high and from 12 to 20 feet in diam- 
eter. (PI. II, B.) The roots of the greasewood serve to retain the 
material forming the mounds, and the obstruction to the wind afforded 
by their branches also tends to preserve them. That the mounds are 
dependent on the greasewood for their preservation is well shown by 
the fact that when the bushes die the mounds soon disappear. In 
some instances a complete sequence can be observed, from large 
mounds crowned with a vigorous growth of greasewood through simi- 
lar mounds on which the bushes are dead, and from those to others 
partially denuded by the wind, in which only the roots of the plants 
which formerly grew in them can be found, and from these again to 
low, indefinite hillocks on the desert, and even flat, circular areas 
which reveal the former presence of a mound solely by the fact that 
the surface is slightly softer and perhaps a little more moist than the 
broad, flat area about it. Although greasewood mounds of the nature 
just described are seemingly transient features of the borders of 
playas, they might, in certain situations, survive a change to more 
humid climatic conditions and the areas they occupy, becoming grass 
covered, be transformed into "mound prairies." 
THE LAKES OF ALVORD VALLEY. 
At the foot of the precipitous eastward-facing escarpment of Stein 
Mountain there is a well-defined valley, trending in general about 
northeast and southwest, which is fully 75 miles long, and about 8 
miles wide in its widest part. This valley was evidently at some 
former time apart of a river system, but the topgraphic history of the 
extensive region of which it is a representative part remains to be 
deciphered. 
In the widest part of Alvord Valley, and east of the highest por- 
tion of Stein Mountain, is situated Alvord Desert. This is a mud 
plain or playa throughout most of the year, but in the winter and 
Bull. 217—03 3 
