Wetlands in northern Salt Lake Valley, Salt Lake County, Utah

6The Oquirrh Mountains consist of Paleozoic sedimentaryrocks, predominantly the Oquirrh Formation, and intrusiveand extrusive Cenozoic rocks. The Traverse Mountains arecomposed of Paleozoic sedimentary rocks and Cenozoic volcanics.Salt Lake Valley occupies a graben that is bounded by faultson its east, west, and south sides. Sediments have been fillingthis graben since Tertiary time. The Tertiary and Quaternarybasin fill is up to 4000 feet (1220 m) thick in some areas ofthe valley (Mattick, 1970), and consists of unconsolidated tosemiconsolidated clay, silt, sand, gravel, and tuff. Quaternarysediments in the upper part of the basin fill range from 0 to2000 feet (0–610 m) thick (Arnow and others, 1970). Thedepositional sequence in the basin fill is complex (Marine andPrice, 1964) due to alternating periods of lacustrine and interlacustrineconditions during the late Tertiary and Quaternary.During the lacustrine periods, or deep-lake cycles (figure 4),much of Salt Lake Valley was covered with water and offshoresilt and clay were deposited in the central parts of thevalley while deltaic (at the mouths of canyons) and nearshoresand and gravel were deposited along valley margins. Duringinterlacustrine periods, sediments were deposited primarilyas alluvial fans at canyon mouths and as fluvial-channel andfloodplain sediments in the central parts of the valley. As ageneral rule, coarser grained sediments exist near valley marginsand finer grained sediments exist in the middle and northend of the valley.ClimateThe climate in Salt Lake Valley can be described as semiaridwith hot summers and moderately cold winters. Due to thelocal topography and the great relief between the mountainsand valley, the weather can be quite variable and is very muchUtah Geological Surveyrelated to orographic effects and local weather patterns (Murphy,1981). The mountains surrounding the valley typicallyreceive substantially more precipitation and have cooler temperaturesthan the valley, and the southeast part of Salt LakeCounty receives the most precipitation.In Salt Lake County, 24 weather stations are or have beenoperated by the Utah Climate Center, and Moller and Gillies(2008) provide information for nine of these stations. Basedon data collected from those weather stations, Salt Lake Valleyreceives between 13.74 and 25.79 inches (34.9 and 65.5 cm)of precipitation annually, at the Draper Point of the Mountainand Cottonwood Weir stations, respectively. The mountainsreceive much more precipitation; the Alta station (elevation8730 feet [2661 m]) receives 58.28 inches (148.03 cm) of precipitationannually.Temperatures in Salt Lake County are also quite variable, andlike precipitation, are related to elevation; the mountains are10 to 15˚F (5 to 8˚C) cooler than the valley. To illustrate theseextremes, the Salt Lake City International Airport station hasan elevation of 4225 feet (1288 m) and a normal maximumtemperature, normal minimum temperature, normal meantemperature, and record high temperature of 64.0, 41.2, 52.6,and 107.0˚F (17.8, 5.1, 11.4, and 41.7˚C), respectively. Incontrast, the Alta station has an elevation of 8730 feet (2661m) and a normal maximum temperature, normal minimumtemperature, normal mean temperature, and record high temperatureof 47.8, 28.7, 38.2, and 94.0˚F (8.8, -1.8, 3.4, and34.4˚C), respectively (Moller and Gillies, 2008).Evapotranspiration is dependent upon solar radiation, temperature,wind, and humidity, but does not directly correlatewith elevation like temperature and precipitation, at least inSalt Lake County. The Draper Point of the Mountain stationFigure 4. Schematic diagram of probable lake levels in the Bonneville basin during the past170,000 years. Modified from Machette and others (1992); note breaks in temporal scale.