5° 



BOTANICAL GAZETTE 



■ [JULY 



of the river, but it by no means exhausts the interesting features of 

 the region. If the low-lying contiguous areas to the westward capable 

 of being flooded are included, the delta may be said to have an 

 area approximately equal to the state of Connecticut. One arm 

 extends over 200 km to the northwestward and includes the Salton 

 Basin, with its exposed bottom more than 130™ below the level of 

 tlie sea. Although the summer Hoods of extreme height find their 



Fig. 2. — View of Rio Colorado at a point where it cuts into the desert mesa of 

 Sonora a few kilometers south of international boundary; looking downstream; Populus 

 and Salix on right hank; dense forest of Populus in background on left bank; portion 

 of mesa in foreground on left bank with Covillea, Stillingia, and Ephedra; Station 3. 



way by old channels into this basin, creating a temporary lake of 

 great extent, yet the district affected must be classed as desert, since 

 the highly saline character of the soil and prevailing low humidity 

 and precipitation support representative types of vegetation (fig. 4).° 

 Other basins ordinarily dry, with saline deposits, are to be found in 

 various parts of the depressed area, which has the characteristics of 

 a sea-floor of comparatively recent date. 



9 See also COVILLE and MacDougal, The Desert Botanical Laboratory of the 

 Carnegie Institution (November 1903), pp. 21-22. pis. 2J-26. 



