Lake Tecopa
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35°52′30″N 116°15′00″W / 35.87500°N 116.25000°W[1] Lake Tecopa is a former lake in Inyo County, southern California. It developed during the Miocene and the Pleistocene within a tectonic basin close to the border with Nevada. Fed by the Amargosa River and some neighbouring washes, it eventually culminated to a surface area of 235 square kilometres (91 sq mi) around 186,000 years ago and left sediments. Afterwards, the Amargosa River cut a gorge out of the lake and into Death Valley with its Lake Manly, draining the lake. The present-day towns of Shoshone, California and Tecopa, California lie within the basin of the former lake.
Lake Tecopa occupied the Tecopa Valley, a pear-shaped valley east of southern Death Valley,[2] in Inyo County, California. The cities of Barstow, California and Las Vegas, Nevada lie close to the lake basin.[3][4] The lake itself had a roughly triangular shape with a northern, a southwestern and a southeastern corner,[1] and at its highstand it covered about 235 square kilometres (91 sq mi).[5] Outcrops of lake sediments occupy a length of 22.5 kilometres (14.0 mi) along the Amargosa River and are 17.7 kilometres (11.0 mi) wide at their broadest.[3] Its southern margin is not clear, given that the height of the sill to the China Ranch basin is undetermined.[6] Several islands existed in Lake Tecopa. Of these, the largest was close to Tecopa, California, and two smaller ones were north of Shoshone, California.[7] The shores of the lake featured marshes and deltas where Amargosa River or spring water entered the lake,[8] as well as freshwater ponds where springs and streams flowed into Lake Tecopa.[9]
At the time of the Bishop Tuff eruption, Lake Tecopa was about 100 metres (330 ft) deep.[10] The waters of the lake were salty and had a high pH,[11][10] inducing precipitation of calcite in the northern part of the lake where the Amargosa River flowed into it.[12] There is some indication that the centre of the lake was much more saline than its shores.[13] Salt lakes generally form when a lake has no outlet, so evaporation concentrates salts in the lake water until the lake contains saltwater.[14]
The Amargosa River flowed into Lake Tecopa, which was the river's terminal lake.[15][10] Most of the water in Lake Tecopa came from the Amargosa River and to a lesser degree from the washes that drain Chicago Valley and Greenwater Valley;[16][17] the total size of its catchment was about 8,300 square kilometres (3,200 sq mi) and most of its water originated in Paiute Mesa, Shoshone Mountains, Timber Mountains and Yucca Mountains.[18][5]
The catchment of the Amargosa River above Tecopa, California is presently about 8,000 square kilometres (3,100 sq mi). Later, after Lake Tecopa had disappeared, the river reached Death Valley and its Lake Manly,[10] dramatically increasing the supply of water to the latter.[19] Presently, the river is largely ephemeral except where it is fed by springs.[17]
Geography
The former lake basin is surrounded by various hills and mountain ranges, formed by rocks of Neoproterozoic to Tertiary age. [10][20] Clockwise from north they are the Resting Spring Range, the Nopah Range, the Sperry Hills, the Ibex Hills, the Greenwater Valley and the Dublin Hills;[21] together they enclose an area of about 500 square kilometres (190 sq mi).[22] The region belongs to the Basin and Range Province of the western United States,[4] where short ranges of mountains lie between plains.[3] This geology consists of normal faults which separate grabens from horsts.[23] It was affected by extensive tectonic activity in the past and may be still active in the present.[24]
Presently, the towns of Shoshone, California, Tecopa Hot Springs, California and Tecopa, California lie within the former bed of Lake Tecopa. California State Route 127 and California State Route 178 cross the lake basin from southwest to north and from west to east, respectively,[21] while the Furnace Creek Road traverses it from northwest to southeast.[25] The terrain of the region is characterized by badlands and rugged mountains with little vegetation away from springs.[17] A number of springs form oases in the area, including the locations of the three towns.[26]
Climate
Presently, the area of Lake Tecopa is a hot, dry desert with most precipitation occurring during summer. In Shoshone, California average temperatures are 19.5 °C (67.1 °F) and often exceed 45 °C (113 °F), with about 70 millimetres per year (2.8 in/year) of rainfall.[27][2] Under present-day climates, evaporation is too high and precipitation too low to allow the formation of lakes in the area.[9] 180,000 years before present, precipitation increased to 200–250 millimetres per year (7.9–9.8 in/year) and average temperatures decreased by 10.5 °C (50.9 °F), lifting the regional water tables.[27]
