40 BOTANICAL FEATURES OF NORTH AMERICAN DESERTS. 
of pools found in their beds long after the flood-waters had subsided were 
a very important factor in desert travel. 
In 1904, however, an irrigation system was instituted to Lentl the 
water from the river around onto a vast area of the slopeof the basin, 
which was found to be unusually fertile and which was rapidly occupied 
with settlers. Canals and openings were connected with the river 
without proper headworks, with the result that the water rushed in with 
great cutting power and deepened the channels to such an extent that 
the entire current of the river was diverted into the basin for several 
months, inundating 500 square miles of desert and forming a lake, the 
deepest part of which gave soundings of 84 feet (plate 41). 
The fresh water thus poured into the basin took up the salts from the 
saline and alkaline soils, with the result that when the inflow of the river 
was checked, February 10, 1907, a total solid content of one-third of one 
per cent was present. 
A detailed analysis of the salts taken up by the fresh water poured into 
the basin reveals the fact that their total composition resembles that of 
condensed river-water rather than sea-water. This agrees perfectly with 
the supposition that since the last waters from the Gulf evaporated in 
this basin directly after connection had been closed by alluvial deposits 
the river has poured flood-water into the basin scores, perhaps hundreds, 
of times, and: with it much salt, so that the bottom of the ancient head of 
the Gulf has been buried beneath a layer of river deposits, and that on 
top and with this deposit are the salts from the river, which are now redis- 
solved by the present flood. 
Preliminary examinations having already been made, the lake was 
circumnavigated at this time by an expedition from the Desert Laboratory, 
and localities selected for the observation of the movements of vegetation 
as the waters receded by evaporation. Among the major phenomena to 
be critically examined are possible introductions by reason of the inflow 
of the river-current, and the manner in which the submerged portion of 
the basin will be reoccupied by the plants that formerly inhabited it. 
Fortunately the bottom of the basin had been examined in 1903 and a 
sketch of the vegetation made as it then existed, which will afford some 
basis for comparison (plate 42). 
THE CUCOPA MOUNTAINS AND THE PATTIE BASIN. 
To the northward of the Cucopa Mountains lies the depression of the 
Salton Basin which is subject to flooding; to the eastward is the strait 
which formerly connected this basin with the Gulf of California, and 
which is now a part of the delta of the Colorado River. As the water in 
the various channels makes its way across the delta it comes against the 
eastern base of the mountains and gathers in the Hardy River, the current 
of which actually bathes the foot of the rocky slopes in places (plate 34). 
