100 THE SALTON SEA. 



schoUii and P. emoryi are very abundant, and there is considerable Croton californicus 

 and Bebbia juncea. Among plants seen only in this association are Chorizanthie rigida, 

 species of Eriogonum, ChamoEsyce serpens, Helianthus tephrodes, and Encelea farinosa. 

 Atriplex hymenelytra and Cladothrix oblongifolia are abundant here but are seldom seen 

 elsewhere. 



IMPERIAL ASSOCIATION. 



The association of the Imperial clays is distinguished by its much sparser plant popu- 

 lation, made up of fewer species. Atriplex canescens is by far the most abundant plant, 

 and a low form of Isocoma veneta, with condensed inflorescence, is also common. Sphce- 

 rcdcea orcuUii, a suffrutescent endemic species, 2 or 3 feet high and flowering the most 

 of the year, is confined to this association. The only trees, and those mostly in the extreme 

 south, are the two species of Prosopis. Where the soil is wetted, under present conditions 

 moBtly by leakage from irrigation canals, Bouteloua arenosa and Lepidium lasiocarpum 

 appear in abundance. In some parts there are considerable societies of Larrea. 



MOUND ASSOCIATION. 



The principal plants of the mounds at the southern border of the Sink are Prosopis 

 glandulosa and Larrea tridentata. Both are deeply buried in the loose drifting material 

 of the mounds, the former without apparent detriment to its vitality, but the latter to its 

 ultimate death. Baccharis sarothroides, a compact evergreen shrub, 3 or 4 feet high, is 

 confined to this association. The annuals Pedis papposa, Chamcesyce setiloba, Baileya 

 pauciradiata, and Palafoxia linearis are more frequently seen here than elsewhere. The 

 intervals between the ligneous plants are mostly bare. 



TRAVERTINE ROCK. 



Travertine Rock is situated at the northwestern end of the Sink, not far from Fig- 

 tree John, and a mile or more from the present shore of the Sea. Seen from a distance it 

 appears to be the culmination of a projecting spur of the western mountains, but it is, in 

 reality, separated from them by a broad expanse of sandy wash, which continues past it 

 towards the Sea, bordered by the usual groups of Parosela spinosa. The rock is a precipi- 

 tous mass of light-colored quartzose, nearly 300 feet high. Its base is heaped about with 

 great angular blocks which have fallen from it. In the far-off time when Lake Cahuilla 

 filled the Sink to its brim, the sharp summit of Travertine Rock projected some 25 feet 

 above its waters. All the once submerged part is coated with gray travertine, 1 to 20 

 inches thick. A distinct horizontal line divides the travertine from the whitish quartzose 

 above and records the former high-water level. 



A few small palo verdes are rooted in the sand at the base, and all about grow the gray 

 shrubs of the desert. Travertine Rock itself is almost destitute of any vegetation, but the 

 little there is has the interest of introducing within the Sink Hmits a few migrant plants 

 conmion in the neighboring desert mountains. The interstices of the tuberculated surface 

 of the travertine contain, in a few places, a minute black lichen, infertile, and which could 

 not be identified, but resembling one seen in Red Cafion. In sand pockets among the fallen 

 blocks about the base grow sparse tufts of Stipa, and in the crevices a few specimens of 

 Nicoliana Irigonophylla, Hqfmeisteria pluriseta, and Peucephalum schottii, the first two 

 chasmophytes, and all common in the canons of the adjacent mountains. 



