THE TUFA DEPOSITS OF THE SALTON SINK. 81 



THE TUFAS OF BLAKE SEA. 



The ancient lake, Blake Sea, that formerly filled the Salton Basin, left among the 

 other records of its existence an extensive tufa deposit. As is the case with the present 

 tufa, it is limited in its distribution to the localities where the waters bathed resistant 

 material. The older tufa is found only along the northwestern shore, where the granites 

 of the Santa Rosa Mountains were washed by the sea. The principal deposit is displayed 

 at Travertine Point, although tufa is found on the cliffs and on boulders of granite scat- 

 tered over the desert sands for several miles to the south. At the time of the Blake Sea, 

 Travertine Point was a low-lying serrate spur or group of granitic hills extending in a 

 semicircle a half mile to the northeast from the mountains. These were submerged by the 

 rising waters until only a few feet remained above the surface of the sea. During the time 

 that the water stood at its highest level, bars of granitic sand were built out from the shore 

 until as the waters began to subside the hills had been connected with each other and the 

 shore as typical land-tied islands. 



With the retreat of the sea the slopes of the bars were slightly notched by the waves, 

 leaving many distinct recessional terraces. Although these were cut but a short distance 

 in the yielding sand, there has not been sufficient wind erosion since to efface them and 

 they are practically as the sea left them. 



At the outermost of these land-tied islands, the original granite hill rose abruptly 

 some 175 feet from the desert sands at its base. Its sheer cliffs were concealed nearly to 

 the top by a steep talus composed of huge boulders up to 10 feet in diameter that had 

 broken and fallen from the cliff. In the cave-like recesses left between the boulders one 

 may penetrate at times 25 or more feet from the surface of the cliff. 



The tufa covers the boulders on all surfaces where they are not in contact. It is 

 dendritic in character and at first sight seems to be a vegetative growth fixed through 

 petrifaction on the surfaces of the rocks. The illusion is heightened by the tendency of 

 the projecting columns and spurs to turn upward and outward towards the light. 



On the outer surfaces of the boulders the tufa is uniformly about 30 inches thick 

 over a vertical range of 120 feet. In places the growing tufa had evidently been broken 

 from the rocks by the waves and the vacant space healed over by a fresh growth, leaving 

 abrupt local changes in the thickness of the deposit. These were entirely local and meas- 

 ured by a few feet, with no relation either to each other or to vertical distribution. 



At the base of the cliff the tufa rather abruptly diminished in thickness, probably 

 due to the recession of the water. At the top a mere film near the high-water mark indi- 

 cated the first deposition of tufa. Within 4 feet of the high-water mark the tufa was well 

 developed and several inches in thickness. 



Around the sides and back into the recesses it diminishes in thickness, until in the 

 darker places it is but a mere film and has lost its dendritic character. Here it is a solid, 

 thinly banded coating similar to the lithoid tufa of the Lahontan Basin. The gradation 

 between the lithoid and dendritic types is gradual, the projecting columns and plates of 

 the dendritic tufa decreasing in size and becoming less prominent with the decrease in the 

 thickness of the deposit until the uniform lithoid coating results. 



The dendritic tufa is occasionally banded, due to a greater coalescence of the indi- 

 vidual columns forming the tufa, but there seemed to be no definite relation either in the 

 distance between the bands or in their number at different parts of the deposit. Con- 

 siderable sand is intermingled with the tufa, in part blown in by the winds since the retreat 

 of the water, and in part included in the tufa and cemented by it. Many snail shells are 

 inclosed by the dendritic tufa, showing that they lived at the time of the formation of the 

 tufa. The lithoid tufa was much purer, containing little if any sand and none of the shells. 



On breaking the tufa it is seen to be built up of rudely circular columns or thin plates 

 approximately 3 mm. in thickness. The interior of these is composed of a finely crystalline 



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