FISSURE IN THE GRANITE—EARTHQUAKES—SALSES. 115 
obtaining a section of the butte, and it exposes a series of inclined strata resting at an angle of 
about thirty-five degrees against the granite. The following sketch represents the outline and 
appearance of the south wall of the break through the butte: 
SECTION ON THE BANK OF THE COLORADO. 
g, Porphyritic granite. s, Inclined strata. a, Alluvium. 
The inclined strata dip to the west, and are not found on the eastern, or “up stream,’’ side 
of the granite ; but on the western or lower side they occur similarly on each bank of the river. 
These strata are, apparently, composed of blocks and fragments of the same granite upon which 
they lie, and seem to have been derived from its degradation. "They are not much water-worn, 
and are rudely stratified, alternating with beds of light-colored clay and gravel formed of the 
same rocks. 
This singular formation probably does not extend beyond the butte, and the appearances indi- 
cate that the materials were laid down in their present inclined position. If so, rapid currents 
must have acted on this granite barrier when it was at a lower level than now. The position of 
the debris involves the necessity of believing that the currents flowed from east to west, or in the 
same direction as the river. It does not appear possible that the deep gap, with nearly vertical 
walls, through which the river now flows, can be the result of degradation by the stream, even 
if the gradual elevation of the rock be allowed. The butte being the only elevated ground 
within a circuit of seven or eight miles, and being surrounded by loose, sedimentary formations, 
we would naturally expect the river to form a channel around the barrier, instead of cutting 
through it. I am therefore disposed to consider this caiion as a deep fissure, resulting from 
volcanic disturbances. 
Earthquakes.—Fort Yuma and its vicinity appears to have been particularly liable to volcanic 
disturbances or earthquakes, for many have been experienced since the establishment of the 
military post. On the 9th of November, 1852, the camp was violently shaken by an earth- 
quake, and the shocks continued almost daily for several months after, and were so frequent 
and expected as not to excite remark. At the time of our visit the shocks had not entirely 
ceased, and I was informed that they had become “quite rare, none having been felt for fully 
three weeks!" The first shock threw down a portion of Chimney Peak, and opened fissures and 
cracks in the clay strata of the Desert bordering the Colorado. At the same time, Major Heint- 
zleman, the commanding officer of the post, observed a column of steam rising from the Desert, 
in a southwesterly direction, at the distance of about forty miles. Several weeks afterwards, he 
visited and examined the locality, and found a small mud volcano, in an active state.! Puffs 
and jets of steam, mingled with large masses of black mud, were being constantly ejected to 
the height of thirty or forty feet. The orifice was in a shallow basin, partly filled with water, 
Covering a surface of severalacres. "This was violently thrown outwards, in waves, at the time 
of each explosion; its temperature was found by Major H. to be 108°. Numerous little cones 
were puffing out steam, like the exhaust of a small high-pressure steam engine ; and in one of 
these, where gas and steam were issuing, the thermometer indicated a temperature of 170? Fahr. 
Another mud volcano was found about the same time, in the northwestern part of the Desert, 
! See Map of the Desert for the position of this volcano. 
