86 THE SALTON SEA. 



and a longer article, from the same pen, forms the introduction to the fifth volume of the 

 report. In both papers a few paragraphs are devoted to the vegetation about New River. 



In 1853 Dr. W. P. Blake made a survey for the proposed Pacific Railroad, which 

 passed through the western border of the Sink. Over much of this route he was the first 

 explorer, but his account, while interesting for the geologist, contains little for the botanist. 

 There are some references to plants of the basin in Torrey's Appendix. Blake's report 

 forms a part of volume 5 of the series of Pacific Railroad Reports. 



Dr. E. L. Greene made a pedestrian journey in February 1877 from San Diego to 

 Fort Yuma, along the old stage route, passing through the New River country. He gave 

 an account of his journey in the American Naturalist, vol. xiv, pp. 787-793, 1880, and 

 vol. xv, pp. 24-32, 1881, under the title "Botanizing in the Colorado Desert." 



A report on the "Lands of the Colorado Desert in the Salton Basin" was published 

 in 1902, as Bulletin 140 of the Agricultural Experiment Station of the University of Cali- 

 fornia. It is devoted to an investigation of the agricultural capabilities of the soil, but 

 contains an annotated list, contributed by J. Burtt Davy, of 22 species of plants collected 

 in Imperial Valley by F. J. Snow, who had made the examination of the soils. 



A brief but valuable account of the botanical aspect of Salton Sink, shortly before 

 its recent inundation, is given by Coville and MacDougal in Carnegie Institution Publi- 

 cation No. 6, pp. 20-22, pi. 23-26, 1903. 



The following recent papers by MacDougal contain much information bearing upon 

 present conditions in the Salton Sink and the Colorado Delta: 



The Delta of the Rio Colorado. Bull. Amer. Geograph. Society, vol. xxxvm, pp. 1-16; map and figures. 1906. 

 Vegetation of the Salton Basin. Fifth Year Book Cam. Instit. of Wash., pp. 119, 170, pi. 10, 11. 1907. 

 Movements of Vegetation in the Salton Basin. Eighth Year Book Cam. Instit. of Wash., pp. 57, 58. 1908. 

 Surface Geology and Vegetation of Salton Basin. Tenth Year Book Cam. Instit. of Wash., pp. 49, 50. 1910. 

 The Desert Basins of the Colorado Delta. Bull. Amer. Geograph. Soc, vol. xxxix, pp. 1-25, figs. 1-11, map. 1907. 



ZONAL POSITION OF THE FLORA OF THE SINK. 



Before entering upon a discussion of the flora of the Sink, it is desirable to indicate 

 the position which it occupies in relation to the general scheme of plant distribution in the 

 Colorado Desert. This will be best understood by a short account of the several floral 

 zones traversed in passing from the northwestern rim of the Colorado Desert at Banning 

 to the dunes which border the sea-level line near Indio, and then considering the zones 

 which intervene between the southeastern margin of the Sink and the Colorado River. 



At Banning, altitude 2,300 feet above sea-level, begins a tension zone in which the 

 plants of the desert contend for the possession of the soil with those which have crossed 

 over from the coastal slope of the San Gorgonio Pass. Rapidly the species of the latter 

 contingent are forced to drop out, and are replaced by successive reinforcements from the 

 former. The ground is fully occupied, and while woody and suffruticose plants are most 

 prominent, there are many perennial and annual herbs, including grasses. 



This tension zone is a narrow one, and already at Cabezon, only 5 miles from Ban- 

 ning, but 540 feet lower in altitude, it begins to be succeeded by an Opuntia- Yucca zone. 

 The dominant plants are Yucca mohavensis, an inornate tree, 10 to 20 feet high, clothed 

 with dagger-like leaves, and Opuntia echinocarpa, here a robust shrub of upright growth, 

 its numerous branches forming a compact head. Subordinate to these are many low', 

 xerophytic shrubs, in the shelter of which, and in the intervals, herbaceous vegetation 

 finds a place. The soil is less closely occupied than in the tension zone, and only here and 

 there is to be found an intruder from the west. The aspect is distinctly desert-like. 



First the Opuntia thins out, and then the Yucca, and the creosote bush (Larrea tri- 

 dentata) becomes increasingly abundant, until at Whitewater, a further descent of 650 

 feet m a distance of 10 miles, it is the dominant plant of a well-defined Larrea zone. In- 

 dividuals of this species are to be found scattered over most parts of the desert beyond, 



