22 BULLETIN 54, IT, s. DEPAETMENT OF AGEICULTURE. 



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 

 imbroken 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 Moimtains, and a low divide, probably allu\dal, in the Juab 

 A'alley at the same latitude. This southern half of the trough is occupied by the 

 northward-flowing Se\der River, which, paralleling the behavior of the Humboldt, 

 turns westward across the north end of the Canyon I^Iountains through 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 

 Se\'ier 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 for a 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 Se\T.er 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.^ 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 email structural basin of the type of the ^^Tiite 

 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 this inquiry. 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. 



1 U. S. Geol. Sur., Monog. I, j). ISl (IS'JO). 



