CHAPTER XVI. 
OBSERVATIONS ON THE SOUTHERN PART OE THE GREAT BASIN. 
Boundaries or the basin as originally assigned.—Supposed dividing range.—Mojave river not a tributary op the Colorado.— 
Boundaries according to recent explorations.—Length and breadth.—Geological structure op the southern portion.— 
Aspect of the region from the crest of the sierra Nevada.—Influence of the sierra Nevada on the climate.—Lost moun¬ 
tains.—Elevation op the surface.—Aspect op the boundary ranges from the plateau.—Slopes.—Channels or valleys in the 
slopes.—Inclination op the slopes.—Lowest parts of the basin.—Mean elevation of the surface.—Geological structure of 
THE LOST MOUNTAINS.-METAMORPHIC ROCKS AT THE MOJAVE.-GRAY GRANITE.—PORPHYRY AND VOLCANIC ROCKS.—STBATIFIED FORMA¬ 
TIONS, slopes.—Tertiary strata and drift.—Rivers and their action on the slopes.—Dry lake-beds.—Mirage.—Prints on the 
CLAY, LIKE TRACKS.-WHIRLWINDS OF DUST'—STREAMS AND SPRINGS.-MOJAVE RIVER, ITS ALTERNATE APPEARANCE AND DISAPPEAR¬ 
ANCE.—Johnson’s river.—Springs near the lost mountains.—Spring at the mojave, and beyond.—Artesian wells.—Observa¬ 
tions ON THE VEGETATION, AND DISTRIBUTION OF PLANTS. 
The extensive semi-desert region east of the crest of the Sierra Nevada, and lying between 
that chain and the mountains hounding the Valley of the Colorado to its sources, is described 
by Colonel J. C. Fremont as an elevated region, surrounded by high mountain ranges, including 
lakes and rivers, which have no connexion with the sea. To this broad area he gave the name 
Great Basin, and has defined its boundaries on the map which accompanies his report made in 
1845. 1 According to this map, the Basin extends from near the parallel of 45° on the north to 
34° 30' on the south ; and east and west from longitude 112° to longitude 120°, (near the 
parallel of 44°, which intersects the Great Salt Lake.) In a subsequent memoir, 2 accompanying 
a map of Oregon and California, published in 1848, the Basin is said to have an extent of about 
five hundred miles in diameter every way. The boundaries, however, as given on the map, are 
very different from those of the map of 1845 ; the southern limit of the Basin being supposed to 
be formed by a dividing range of mountains, extending nearly east and west along the parallel 
of 38°, called the “ Dividing range between the waters of the Pacific and the waters of the Great 
Basin.” The northern boundary was also represented as far south as the parallel of 41° 30'. 
The Mojave river was then believed to be a tributary of tbe Colorado, and was so represented. 
It was also laid down on the “ Bureau Map ” of 1850 3 as a continuous river from its sources to 
the Colorado, receiving, as a tributary, a stream called Agua de Tomaso. Under the supposition 
that the Mojave river drained into the Colorado, it was necessary to exclude from the limits of 
the Great Basin a large area at the south, thus leaving its southern boundary uncertain, 
although apparently formed by mountains seen in the north—the dividing range of the map of 
of 1848. 
It having been ascertained by the Expedition that the Mojave is not a tributary of the Colo¬ 
rado, but that it ends in a dry lake nearly one hundred miles distant from the Colorado, and 
that a high and rugged range of mountains forms a barrier between the two rivers, the basin- 
1 Report of the Exploring Expedition to the Rocky Mountains, and to Oregon and to North California, House Doc. No. 
166, 1845. 
2 Geographical memoir upon Upper California, to illustrate the map of Oregon and California. Senate, 30th Congress, 
Miscellaneous No. 148, p, 7. 
3 Map of the United States and their Territories, compiled in the Bureau of Topographical Engineers, Washington, 1850. 
