The purpose of this guidebook is to summarize the geology and mineral development history of the Salton Sea Area and to relate that geology and history to the evolution of other resources and scientific disciplines. REPORT ORGANIZATION Part 1: TEXT FOR FIELD TRIP GUIDEBOOK Part 2: AREA MAPS (Maps A1 to A16) FOR FIELD TRIP GUIDEBOOK These maps are at 1:50.000 scale and adapted from the Regional Geologic Mosaic. They are tabloid size (11" x 17"). Part 3 of this paper are the Regional Maps. They are designed to be printed on Arch E size paper (32" x 46"). -Map B: Regional Geology (USGS) 750K -Map C1: Regional Geologic Mosaic (various original scales) -Map C2: Regional Geologic Index Map -Map D: Regional Mineral Resources -Map E: Regional Environmental Resources -Map F: Regional Land Status and PLSS Part 4: APPENDICIES Part 4 of this paper are the data appendices. A. MINES B. THERMAL SPRINGS AND WELLS Part 5: MINE DESCRIPTIONS AND SUMMARY Part 5 of this paper is a set of separate articles for each producing mine, past producing mine or mineral occurrence of special interest in the study area. This summary and alphabetical listing has URL links to Academia.com.

Note: Imperial Salt Works was also known as the Western Salt Company. LOCATION 10S 13E Sec. 06 SBM 33.33478000030 -115.65415000000 (MRDS, 2011). 10S 13E Sec. 06 SBM 33.33615999960 -115.65772000000 (MRDS, 2011). Morton (1977) describes the now-submerged location for the Imperial Salt Works Plant: This mineral extraction operation was in the N1/2 Sec. 6, T.10S, R.13E, SBM, Frink quadrangle 7.5 minutes, along the southeast shore of Salton Sea, 12 miles northeast of Niland, 2 miles southwest of Frink Siding. Imperial Irrigation District, El Centro, California (Morton, 1977, p.84-85). The site of the plant is now submerged under rising waters of the Salton Sea. DEVELOPMENT The University of Redlands website (2016) has this history of salt developments on the Salton Sea: Long before there was a Salton Sea, there was salt in the basin. The floor of the basin, which is an extension of the Gulf of California, is almost 275 feet below sea level. The salt deposits, first discovered in 1853, alternated between a salt marsh and a bed of dry salt as weather conditions and inflow from the Colorado changed. Although the salt deposits were well known and utilized by local Native Americans, it wasn't until 1884 that commercial production began. The New Liverpool Salt Company began operations on the north end of the basin scraping the salt crust with plows. The rock salt deposit covered 1,000 acres and produced 2,000 tons of salt a year. The operation consisted of plows guided by local Cahuilla Indians that cut a wide shallow furrow in the crust. The salt piled in ridges on either side of the furrow and was raked into piles and transported to mills. Each plow could harvest 700 tons of salt a day. At the mill, the salt was reduced in size by breakers where it was then ground, cleaned, graded, and sacked. The salt was used by factories, dairies, druggists, and for table use and sold for $6 to $36 per ton depending on grade. In 1905, flooding destroyed the New Liverpool Salt Works. There was no other attempt at salt production in the basin until 1919 when The Mullet Island Paint Company produced a small amount of salt from hot springs. In 1934 the Mullet Island Development Company obtained salt from salty wells in the basin. The Mullet Island Salt Works of the Reeder Salt Company operated three evaporation ponds from 1940 to 1942 on land leased from the Imperial Irrigation District, which supplied salt for local icing and refrigeration cars. From 1927 to 1930 Seth Hartley operated four concentration ponds near Mecca and experimented with solar evaporation ponds near Caleb. In 1935 Seth and Chester Hartley opened The Imperial Salt Company, the biggest of the salt operations, on land leased from the Imperial Irrigation District near Frink. It was bought by the Western Salt Company in 1942. Before closing in 1947 it reported the production of 16,000 tons of salt per year from 175 acres of evaporation ponds. (From http://www.spatial.redlands.edu/salton/Downloads/Shapefiles/Metadata/ss_saltworks_metadata.htm accessed Aug. 7, 2016). Morton (1977) provided this development history for the Imperial Salt Works: The Imperial Salt Works was begun by Seth Hartley and his son Chester Hartley in the early 1930's. First production was recorded in 1935. The plant was purchased in 1943 by the Western Salt Company. The operation was abandoned in 1947 after difficulties with sodium sulfate. The water level in 1962 was above that of the levees of the ponds. Salt was obtained through a process of crystallizing by solar evaporation of Salton Sea brine. The brine was drawn from the lake through a canal and pumped to two separate series of nine ponds each. Gravity flow from one concentrating pond to another was achieved through use of gates between levees. Final concentration before withdrawing the pickle to the crystallizing ponds was 28.95 percent Be*. Harvesting was done once a year by dragline scraper into side dump rail cars. Plant capacity was 16,000 tons per year from a total of 160 acres of concentrating ponds and about 15 acres of crystallizing pond. (Sampson and Tucker, 1942:138; Ver Planck, 1957:486; Ver Plank, 1958:73-74, 115; Morton, 1977, p.84-85). * I am not sure what the Be in this context means. Maybe it is a typo for Na. GEOLOGY AND MINERALOGY Morton (1977) gave the following discussion of salt mineralogy: In 1970 the Salton Sea, a dry lake before the advent of irrigation in Imperial Valley, had an estimated salinity content of 37,500 parts per million, more saline than sea-water. The brine's composition differs from sea water, however, in its higher sulfate, carbonate, and calcium content and in its slightly lower chloride and magnesium content. The chemical composition of the lake has been quite variable since its formation in 1905-1906. This has been attributed to the initial dissolving process of playa lake salts, the influx of Colorado River water, and gradual leaching of irrigated land in Imperial and Coachella Valleys. The salinity in recent years (circa 1963) has been increasing steadily. Salt was recovered by evaporation of the Salton Sea brines as early as 1919, but the principal period of production was from 1934 through 1944, when both the Mullet Island and Imperial Salt Works were in operation. In all, less than 25,000 tons were produced which was valued at $3 to $4 per ton. Sodium sulfate, occurring principally in the form of the mineral thenardite (Na2S04), has been mined from deformed lacustrine beds of the Borrego Formation of Pliocene age. Natural deposits of sodium sulfate and other "salts" are frequently found in arid regions. The "salts" were originally leached from the surrounding rocks by surface or spring waters and transported to a low point in the interior drainage system. If input exceeded evaporation an alkali lake or pond was formed. If evaporation exceeded input, the water was vaporized and the "salt" remained as a residual deposit, often buried by later sediments. The Bertram deposit, 1 8 miles northwest of Niland, was the only mine developed. It yielded less than 1,000 tons during its three productive years, 1923, 1941, and 1942. Some shipments were made to Berk and Company, a chemical manufacturer in New York. The principal use of sodium sulfate is in the preparation of Kraft pulp for paper-making. Other uses are in detergents, glass-making, and various chemicals. Beginning in 1964, pilot plant investigations were conducted for the recovery of sodium chloride, potassium chloride, and calcium chloride from geothermal steam well brines near Niland. It is believed that the elements in the brines accumulated by intensive leaching of trace quantities from the Cenozoic sedimentary rocks underlying the Salton Trough. Sodium chloride, common salt, is the basic raw material in the chemical industry from which sodium and chlorine compounds are made. Potassium chloride is a source of potash for fertilizers and is used in making other potassium chemicals. Calcium chloride in solid form is a good water absorbent and is used to de-ice roads, to control dust, and to prevent the loss of moisture during the setting and curing of concrete. In liquid form, it is used in a variety of ways, including as an additive to drilling muds (Morton, 1977, p.84-85).

Interim results of a new conceptual modeling effort for the Salton Sea geothermal field (SSGF), in the Salton Trough of southernmost California, show that this resource: (1) is hotter at depth (up to at least 389 degrees Centigrade at 2 km) than initially thought; (2) is probably driven by a still-cooling felsic intrusion rather than (or in addition to) the primitive mafic magmas previously invoked for this role; (3) may be just the most recent phase of hydrothermal activity inititiated at this site as soon as the Trough began to form ~4 m.y. ago; (4) is thermally prograding; and (5) in spite of 30 years' production has yet to experience significant pressure declines. Thick (up to 400 m) intervals of buried extrusive rhyolite are now known to be common in the central SSGF, where temperatures at depth are also the hottest. The considerable thicknesses of these concealed felsic volcanics and the lack of corresponding intermediate-composition igneous rocks imply coeval granitic mag...