GRAVEL AND VOLCANIC FORMATIONS: TUOLUMNE COUNTY. 139 
twenty feet above the general level of the surface, and glistening white in 
the sunlight. It is said that the crevices, or cavities, between the “bould- 
ers” —as the projecting portions of the limestone are called by the miners 
—have in some places been worked down to a depth of a hundred feet; 
the usual depth, however, was much less. Many attempts have been made 
to drain this region by deep tunnels; but they have not, it is believed, been 
in any case pecuniarily successful, owing to their great cost, the peculiar 
nature of the ground, and especially the very irregular form of the bottom 
of the eroded rock. The usual method of mining has been to hoist the 
pay dirt into a dump-box, placed high enough to allow the refuse to be 
carried away in sluices, into which the material was washed by water thrown 
upon it from the hydraulic pipes. The hoisting was done by power obtained 
from the water brought to the spot in pipes, under sufficient pressure to rise 
to the top of the overshot wheels employed. Many stories are told by the 
miners of deep holes in the limestone, resembling caves in their extent and 
ramifications. The material which filled the cavities between the “bould- 
ers,’ in the neighborhood of Columbia, was largely made up of clay, and 
much of it was evidently the result of the trituration of volcanic rocks. 
These deposits have proved to be extremely rich in the bones of various ex- 
tinct animals, especially of the mastodon, as will be noticed farther on. The 
most extensive and interesting locality of mining in the limestone cavities 
is near Columbia, from which place as much as $100,000 per week is said to 
have been shipped in the years between 1853 and 1858. Work was still 
going on there in 1870 and 1871, but on a very limited scale, as compared 
with its former activity. Some claims are said to have paid, for a time, very 
large profits, —as much as $600 per day for each man employed. The 
scene at Knapp’s Ranch, just adjoining Columbia on the east, where the 
“boulders” are very large, was a most extraordinary one, at the time when 
operations were being actively carried on, and could hardly be compared 
with anything else in the way of mining, unless it might be the scene at the 
diamond fields in South Africa, known to the writer, however, only through 
the medium of photographs. The ragged projecting masses of limestone, 
between and among which ran innumerable lines of sluices supported on 
trestles, the lofty wheels mounted on tall scaffolds, with the accompanying 
ladders, ropes, derricks, and other appliances, formed a most striking picture 
of mining activity, displayed in a very peculiar field. 
Kincaid Flat, two miles southeast of Sonora, is also on the limestone belt, 
