24 GEOLOGY. 
lying soft sediments; producing, by this undermining process, the speedy degradation of the 
plain. 
We must consider, also, that when the country was at a lower level, the rivers from the Sierra 
Nevada flowed over the surface of the lava ; and that long before the newly risen continent was 
trod by the Mammoth and Mastodon, anterior to the advent of man, the San Joaquin com- 
menced wearing its crooked channel, and poured its waters into the sea over the precipitous 
edges of the hard basalt. As the country gradually rose up, the clift was undermined ; and 
during the lapse of ages the river must have cut its way backwards and excavated the present 
deep channel. It is thus probable that a series of magnificent waterfalls existed during the 
progress of this backward movement. 
It has already been stated that a large quantity of the river-drift in the bed of the Merced 
river was composed of basalt. The headwaters of this stream are supposed to be near those of the 
San Joaquin ; and I am informed that basaltic rocks form hills of great height in that vicinity. 
It is probable that these are a portion of the field of basalt just described, and they may be near 
or at the original source of the overflow. If this is so, it was probably above the level of the 
former sea ; but the currents of lava that flowed from it may have reached the ocean and spread 
out in a plain on its bed. 
It is difficult, and, indeed, impossible, to determine the former boundaries of. this once 
igneous plain ; it may have reached far out to the westward of its present limits, and extended 
over a part of what is now the Tulare valley. 
The Indians collect about the fort in great numbers during the winter—as many as five or 
six hundred being there at one time. They live in the usual manner—in brush huts—a short 
distance below the fort. They make beautiful baskets or trays, of a strong round grass, which 
they weave so tightly and evenly that the baskets will hold water; and they are sometimes 
used to hold water while it is made to boil by throwing in heated stones. One mile below the 
fortis the ferry across the river. Here, there are several houses and shops; the place being 
called Millerton. The trade is chiefly with emigrants, miners, and the Indians. During our 
stay at this camp, Captain Love, at the head of a party of rangers, arrived, bringing with him 
the head of the notorious robber-chief, Joaquin Muerto. They had surprised - Joaquin, with 
his party, in a pass of the Coast Range, and, after a short fight, shot him through the head. 
The temperature of this valley or, at least, of our camp-ground, is worthy of note. Each 
day was like the preceding, and the unclouded sun seemed to have a remarkable heating power. 
The high hills on each side prevented a free circulation of air and reflected back the heat. The 
thermometer, during the middle part of the day, seldom indicated a temperature lower than 96 
degrees F., and generally stood from 100? to 104° in the shade ; in some localities 115°. 
FORT MILLER TO OCOYA CREEK. 
Fort Miller to King's river, July 31, 25. 13 miles, .— We left the San Joaquin at 4 a. m. of the 
31st, and turned southward over low and rounded hills at the base of the mountains, and, after 
travelling about five miles, came to the plain of the San Joaquin or the Tulare valley. It is 
now more properly the Tulare valley, as the San Joaquin river, after leaving t the foot-hills and 
coursing a short distance down the slope of the valley, turns north ıward and does not receive the 
streams which descend from the mountains further south. The. valley ， or plain, however, 
sr — me there is no visible line ot eme bet: e ~ two systems of 
