636 Part IV. Chapter 5. 
The alkali playas, or flats, are characterized by Allenrolfea (Spirostachys) occidentalis 
and Suaeda, Distichlis spicata, Phragmites phragmites, Juncus Cooperi. In some of the moister 
places occur Scirpus Olneyi and Tessaria borealis. 
To be considered here is a palm Washingtonia (Neowashingtonia) filifera which grows 
in groves in the canyons formed by the timberless spur which juts eastward from the San Bernar- 
dino Mountains?!) in broad deltas of gravel. The palms grow on clay soil incrusted with alkali, 
but their roots receive the water which falls, as rain, on the mountains sinks into the earth and 
percolates down to the foot of the hills. These areas are marked by the presence of plants 
characteristic of alkaline springs. Besides the palm occur Prosopis juliflora, Distichlis spicata, 
Epipactis gigantea, Parosela spinosa, Peucephyllum Schottii. Elsewhere on this desert grow 
ucca mohavensis, Opuntia Bigelowii, O. echinocarpa, O. basilaris and Audibertia (Ramona) poly- 
stachya. 
Delta Sand Mound Formation. The arid region of the Colorado Delta 
extending southward from the Gila River consists principally of long gentle 
slopes or sandy gravelly plains rising gradually toward the interior and broken 
here and there by a series of low mountain ranges. Mounds of sand are found 
held together by the roots of Ephedra, Larrea and other shrubs ?). In addition 
to the few herbaceous types which arise during the season favorable for their 
growth, the principal types are perennials with spinose branches and reduced 
deciduous leaves such as Franseria albicaulis, Lupinus mexicanus, Abronia 
villosa, Astragalus Vaseyi, Plantago. scariosa,-Gilia Schotti, Stillingia annua, 
Asclepias subulata, Hesperocallis montana (with perennial bulbs) and Fouguiera 
splendens. 
’ 
The delta consists of an alluvial plain not more than ı2 feet (4 m) above the low water 
mark. The banks of the river are subject to erosion and are constantly shifting. Almost 
pure assoeiations of willow and poplar, Populus mexicana, cover extensive areas, Large areas 
are also covered by Pluchea sericea, mesquite (Prosopis velutina) and serew-bean (P. pubescens). 
Phragmites fringes the channel in the upper part of the delta and two or three species of Atri- 
plex are found in sections where the action of the river prevents the establishment of woody 
perennials of larger size. Typha angustifolia grows in the lower part of the delta where the 
river is affected by the spring tides in dense masses lining the shore for many miles. The willows 
extend farthest toward salt water. Beyond these are mud plains covered with salt grass (Distichlis 
spicata) and Cressa truxillensis with small clumps of Atriplex, Prosopis velutina and P. pubescens.. 
n other places, according to Mac DouGAL3), the arrow-weed (Pluchea sericea), quelite (Ama- 
ranthus Palmeri), wi emp (Sesbania macrocarpa), salt-grass and wild rice (Uniola Palmeri) occur 
in considerable density. Filling the spaces between the colonies of these plants grow the mesquite 
and screw-bean Phragmites, Scirpus, cow pumpkin (Cucurbita palmata) and others. 
B. Sinaloan District. 
This district occupies that part of Mexico lying between the Gulf of 
California and the Sierra Madre Mountains and extending south almost 
to the twenty fifth degree of latitude, just north of Mazatlan. The prevailing 
1) CoviLte, F. V. and Mac Doucat, D. T.: See Bibliography p. 75. 
2) Mac DoucaL, D. T. (1904): See Bibl. P- 77; SNOW, FRANK J,, Hırcarp, E. W., Shaw, 
G. W.: Lands of the Colorado Delta in the Salton Basin. California Agricultural Experiment 
Station. Bulletin 140 (1902); Mac DouGAL, D. T.: Across Papagueria. Bull. Amer. Geogr. Soc. XL 
Dec. 1908. 
3) Botanical Features of North American Deserts. Publication 99. Carnegie Institution 1908: 33- 
07 
