370 
Journal of Agricultural Research 
Vol. I, No. s 
While no evaporation data are available for Tooele Valley, evaporation 
measurements 1 have been made during the last five years at Nephi, 
about 60 miles south of Tooele. These measurements show that the 
monthly evaporation during June, July, and August is at least double 
that of April and October. (See Table I.) 
Table I .—Evaporation from a free-water surface at Nephi , Utah , during the months of 
April to October , 1908 to 1912. 
Year, 
April. 
May. 
June. 
July. 
August. 
Sep¬ 
tember. 
October. 
TQO& . ... 
Inches. 
Inches. 
Inches. 
7.87 
8.81 
IO. 90 
8. 69 
9. 28 
Inches. 
10. 52 
9 - 47 
9.98 
8. 72 
9. 24 
Inches. 
9 ■ 34 
7 - 03 
10. 09 
10.47 
8. 89 
Inches. 
6. 23 
5 * 59 
6. 01 
6. 69 
6. 16 
Inches. 
I 9°9 . 
1910 . 
1911 . 
1912 . 
Normal. 
3 - 6 4 
5- 82 
4.93 
3 - 54 
5-99 
7.46 
8. 41 
6 . 30 
4 - 43 
3 - 72 
3 - 65 
2. 98 
4. 48 
7.04 
9. II i 
9 - 59 
9. 16 
6. 14 
3 - 70 
Therefore, while the summer months are by no means rainless in this 
locality, the great increase in the rate of evaporation is such that the 
light precipitation can have but little effect upon vegetation. In those 
parts of the valley where the ground water is beyond the reach of the 
plant roots the vegetation becomes dormant after the moisture stored in 
the soil by the winter and spring rains has been exhausted. Herbaceous 
plants ripen and die, at least to the ground, while the woody species, 
losing much of their foliage and reducing their transpiration to a mini¬ 
mum, enter a resting condition which is nearly as complete as that which 
is brought about by the low temperatures of winter. Where there is a 
greater depth of readily permeable soil in which moisture can be stored 
than is ordinarily the case in this valley, the beginning of summer dor¬ 
mancy is longer postponed. On the sand hills the larger shrubs may con¬ 
tinue growing more or less actively throughout the summer. In the 
lower part of the valley, where the ground-water table is high and the 
soil is moist throughout the summer nearly or quite to the surface, 
active growth continues until it is terminated by frosts. 
GEOLOGY AND TOPOGRAPHY OF TOOELE VALLEY 
Geologically, Tooele Valley is of exceptional interest because of its 
occupancy at one time by a bay of Lake Bonneville, a Pleistocene lake, 
the beach lines of which are strikingly in evidence upon the sides of the 
surrounding mountains. The highest of these terraces is 1,000 feet 
above the present surface of Great Salt Lake. An exhaustive study 
of the region has been made by Gilbert. 2 * 
1 Measurements by the Office of Biophysical Investigations in cooperation with the Office of Cereal 
Investigations, Bureau of Plant Industry, and with the Utah Agricultural Experiment Station. 
2 Gilbert, G. K. Lake Bonneville. 438 p., 51 illus., 51 pis. Washington. 1890. (U. S. Geol. Survey 
Monograph 1.) 
