of lava are crowned, especially on the west, by a belt of vol- canoes that rise locally to 19,000 feet with passes at 16,000 feet. So scanty is the vegetation of the Puna that bare rock, sand, and salt reflect the strong sunlight of these high altitudes to the great discomfort of the traveler. Following down the sterile volcanic slopes of its basins one commonly passes over loose alluvium forming a mile-long piedmont fringe, material washed down from the higher slopes about the mountainous basin border. The material of the piedmont fringe becomes progressively finer as one descends, and it ends altogether at the edge of the flat salt-encrusted surface that forms the basin floor. The lower slopes are generally marked by a growth of green, resinous, and fragrant tola shrub; and it is in the belt of tola that the traveler comes upon water if he finds it at all. From an elevated lookout on the trail he may see at long intervals the green and naturally irrigated ribbons that thread the piedmont and mark the sites of tiny streams issuing from springs or seeps on the mid-slope. In many cases the water is brackish or quite salty. Ina few cases, commonly at intervals of twenty to forty miles, sweet water may be found. The tola bushes furnish fuel for the camp fire, and the ribbon of green furnishes pasturage for the mules.
These little natural oases are called vegas, and their location and extent are one of the chief interests of the traveler. In their absence a dry camp must be made, and the mules must go another day without water and subsist upon dry barley, a quantity of which has always to be carried as a necessary part of the supplies. A camp located at such a point will generally have a measure of protection from a ravine bank, cut in the alluvium, and will have in front of it the white floor of the basin, quite flat, with dark patches here and there where open water stands.
Difficulties of the Crossing: The Wind
In the daytime whirlwinds sweep across the piedmont slopes and the salars, lifting their great yellowish white columns of dust to altitudes of a thousand feet and more. Everywhere are signs of the wind in long ridges of wind-blown stuff, pebbly
