Water Supply and Irrigation Papers of the United States Geological Survey . f Volcano Lake. The forms that result from the activity and thephenomena generally are similar to those near Imperial Junction,but on a larger scale. ORIGIN OF THE DESERT LOWLAND. Of the details of the origin of the valley occupied in its southernpart by the Gulf of California and at its northern end by the ColoradoDesert, but little is known. It may be said, however, as a generaliza-tion, that it belongs to a type which physiographers describe as con-structional—that is, it represents an area which has been depresseda
Water Supply and Irrigation Papers of the United States Geological Survey . f Volcano Lake. The forms that result from the activity and thephenomena generally are similar to those near Imperial Junction,but on a larger scale. ORIGIN OF THE DESERT LOWLAND. Of the details of the origin of the valley occupied in its southernpart by the Gulf of California and at its northern end by the ColoradoDesert, but little is known. It may be said, however, as a generaliza-tion, that it belongs to a type which physiographers describe as con-structional—that is, it represents an area which has been depressedas a result of crustal movement, as contrasted with valleys due toerosion. There are many proofs of this. The fact that its rockfloor is below tide, even in those parts north of the gulf where theactual surface is well above sea level, proves that a part at least of itsposition is due to actual subsidence of a block of the earths crust,because erosive action can not extend below the ultimate base levelwhich is usually sea level. Wells drilled near Imperial indicate that.
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