D2, BULLETIN 54, U. S. DEPARTMENT OF AGRICULTURE. 
paratively narrow and is further narrowed by the north-south range of the Mineral 
Mountains, almost equidistant between its sides. Farther to the south it bends 
westward and again expands into another filled valley, the Escalante Desert. 
The easternmost of these three troughs is much more regular and stretches almost 
unbroken from the fortieth parallel to the Arizona line, being bordered on the west 
by the continuous uplift of the Parowan, Tushar, Pavant, and Canyon Ranges and 
on the east by the western scarp of the high plateau country. Essentially this valley 
is but a southward extension of the Jordan and Utah Lake Valleys, the depression 
which lies just beneath the great west scarp of the Wasatch Range. But only the 
southern part of this trough belongs to the Sevier drainage, the parting being the 
local uplift of the Tintic Mountains, and a low divide, probably alluvial, in the Juab 
Valley at the same latitude. This southern half of the trough is occupied by the 
northward-flowing Sevier River, which, paralleling the behavior of the Humboldt, 
turns westward across the north end of the Canyon Mountains uso the deep 
Sevier Canyon and enters the middle or main trough of the basin. 
The westernmost trough is well defined but less than half the length of the others. 
It consists of the Sevier Lake and Preuss Valleys and merges to the north into the 
Sevier Desert. It is interesting mainly because it contains the present deepest 
depression in the basin, the sink of Sevier Lake. 
At the higher stages of Bonneville the middle and western troughs were largely 
filled with the waters of the lake. The eastermost trough is higher and was not filled, 
except fora small embayment at the northern end. It contained a northward-flowing 
river, the predecessor of the present. Sevier, which emptied into this embayment. 
When the waters of Bonneville fell low enough to expose the comparatively low 
divide separating the Sevier Basin from that of the Great Salt Lake, the former con- 
tinued for a time to overflow into the latter through a well-marked channel which 
may still be seen east of McDowell Mountain and which has been described by Gil- 
bert.1. With increasing desiccation the outflow of the Sevier Valley ceased and its 
basin attained the inclosed character which it now exhibits. 
At the present time the central and western troughs have become areas of prac- 
tically no drainage. ‘The northern end of the former—the Preuss Valley— has been 
cut off from Sevier Lake by a low alluvial divide, while the Escalante Desert has been 
similarly separated from the central trough. The eastern trough has more nearly 
retained its original character. The Sevier River is still a fairly vigorous stream until 
it begins to cross the Sevier Desert. Here it loses itself in a succession of meanders 
and local marshes, reaching the lake only in time of flood. It is probable, however, 
that this failure to reach the lake continuously is very recent and due to the large 
use of the waters for irrigation. The Sevier Desert itself is a succession of local 
playas much like the Great Salt Lake Desert, but less saline and more often having 
free but unused drainage channels to the sink. Rush Lake and Parowan Valleys 
east of the Escalante Desert were once freely drained to the main lake body, but 
have been cut off by stream decay and now contain small saline lakes. Round 
Valley, east of the town of Manti, is a small structural basin of the type of the White 
Rush and Cedar Valleys above described. How long it has been a separate drainage 
unit is not fully certain—probably not very long and in any case its area of 170 square 
miles is too little to give it any importance to thisinquiry. At the present time the 
area from which Sevier Lake receives even occasional drainage is probably not over 
10,000 square miles. During Lahontan time the Sevier Basin, including Parowan, 
Rush Lake, Round, and Preuss Valleys, the Escalante Desert, etc., had a total area 
of 16,375 square miles. 
1U. 8. Geol. Sur., Monog. I, p. 181 (1890). 
