348 THE COLORADO DESERT 



As the way leads southward, Signal Mountain, the northern peak 

 of tlie Cocopah range, c]isa})pears from view, l)ut in front appears, ris- 

 ing from the plain, an isolated and striking landmark, the nol^le crater 

 of the Sierra Prieta, called by Americans " Black Butte." Such 

 active eruptions of lava as built up this perfect crater are indeed past, 

 but secondary' volcanic activity is still present in the hot ininei'al 

 springs that surround the Colorado Desert and in the beautiful erui)- 

 tive mud springs or salses, known as mud-volcanoes. These are found 

 in two i)laces on the Colorado Desert — in the Cocopah Valie}' a few 

 miles from Sierra Prieta, and far north, just south of Salton Sea.* 



The whole region of the Sierra Prieta is full of evidence of vecent 

 action. North of the mountain and half a mile from its base are 

 three hillocks, the largest 100 yards long and 50 feet high, which were 

 evidently formed by the eruption of soft mud accompanied by gas. 

 The roclv of these mounds is im})erfect]y hardened mud, full of vesic- 

 ular cavities such as would be formed by the presence of gas in the 

 mud eruption. 'J'he Sierra itself is several hundred feet high, and, 

 with the deposits of broken lava that surround its base, has a circum- 

 ference of seven or eight miles. The rock is scoriaceous lava, with oc- 

 casional basaltic blocks that exhibit an imperfect culumnar structure. 

 The rock of the sides is much broken by weathering, but the edge of 

 the crater is beautifully defined. The floor of the depression is smooth 

 and level and covered with fine clay, evidently blown in by winds. 

 Water at times has stood at considerable depths within the crater. It 

 is 250 paces across the perfectly circular bottom. At the center of the 

 floor a small basin has been scooped out by human hands to collect 

 the last drops of rain water. 



The mud-volcanoes lie on a flat, mud plain south of the Sierra 

 Prieta, and during the overflow are surrounded b}'' the waters of the 

 New and Hardy Rivers and the ''saltslough ; " alsoafew ofthesprings 

 are buried beneath the risen waters of Volcano Lake. At the time of 

 my visit one of these springs was erupting beneath the water, throw- 

 ing U}) mud several feet above the surface with a cannonading that 

 could be heard at a distance of three or four miles. Along the shores 



* Fur ail intereisting clesLTiption of their discovery liy .Major lleintzelmiiii, in lS,'i:2, see Pacific 

 Eaili-oad Reports, vol. v ; "Geological Report," tiy Win. P. Blake, p. 115. See also "An ai> 

 count of some volcanic springs in the Desert of the Colorado in Southern California," by iJr 

 John L. Le Conte, American Journal of Science and Art, 2nd series, vol. xix, May, 18r).=), ana 

 " Notes of a visit to the mud-volcanoes in the Colorado Desert in the month of July, 1857," V)y 

 Dr John Veatch, in the same journal, vol. xxvi, p. 280, 18o8, ami also pulilishi-d in the Proceed- 

 ings of the California Academy of Science, 1857, p. 104. 



