f 







VEGETATION OF AN ALKALINE MARSH. 23 



The surface of an alkaline marsh is likewise devoid of vegetation, but 

 its margin supports iu many cases a luxuriant growth. A section at 

 Bennett Wells, Death Valley, from the salt-marsh to the mesa illustrates 

 the flora of such an area. 



First there occurs a strip, a few meters broad, of Allenrolfea occi- 

 dental! s ; next, a similar strip of Juncus cooperi; and third, a belt 

 of Sporobolus airoid€8 and Pluchea sericea about ,'500 meters broad. 

 Across the second and third belts DisticMis spicata occurs sparingly, 

 mixed with the other plants. Over all three areas the thin alkaline crust 

 on the soil is continuous or nearly so, and there is no loose sand. The 

 fourth belt consists of Prosopis juUflora and Atriplex cancscens, inter- 

 mixed in some cases with Suceda suffrutescens. Sand has drifted into 

 clumps of these plants, so that the ground consists of a succession of 

 dry hummocks, the hollows between them showing either a slight alka- 

 line efflorescence or in some cases an incrustation. At one point this 

 belt is about 750 meters broad. The next belt is made up principally 

 of Atriplex polycarpa, with a few scattered specimens of Larrea triden- 

 tata. The soil is a mixture of gravel and clay, with some visible trace 

 of alkali. The sixth belt is that of Larrea tridentata. The soil is 

 composed of sand and gravel, seldom showing a trace of alkaline de- 

 posit on its surface. Along the margin nearest the preceding belt 

 Atriplex hymenelytra is abundant, while in the other direction Franseria 

 dumosa, Eriogonum inflatiun, Gladothrix oblongifolia, and Hymenoclea 

 sal-sola appear, followed by the other vegetation of the mesa. 



The living springs and streams of the desert are characterized by a 

 still different group of plants. The shrubs and trees common in the 

 vicinity of such places are Populus fremontii, Prosopis pubescens, Salix 

 longi/olia and Salix nigra venulosa. Several perennials, such as Apocy- 

 num cannabinum, Bcrula erecta, Elcocharis rostellata, Juncm baltieus, 

 Nitrophila occidentalism Scirpus lacustris occidentalism 8. olncyij 8. ameri- 

 canus, and Typha angustifolia y are abundant, while Polypogon mon- 

 speliensis is a frequent annual. 



Between a gravelly mesa, a dry lake, an alkaline marsh, and a spring 

 all geological gradations occur, with corresponding combinations in the 

 accompanying plants. 



As stated in an earlier paragraph, certain of the desert mountain 

 ranges between the Sierra Nevada and the Colorado River rise to a 

 sufficient altitude to be crowned with coniferous timber. The flora of 

 these areas differs from that of the desert proper in the possession not 

 only of arboreal vegetation, but also of a different group of shrubs and 

 herbaceous plants. A belt of Pinus monophylla, about 600 meters in 

 thickness, constitutes the lower part of this timbered area and, together 

 with Juniperus californica utahensis 7 which mingles with the piilon and 

 often extends 50 meters below it, marks a zone that has been denomi- 

 nated the Upper Sonoran. 



