April 4, 1863: Durham’s Ferry
[Today] we pushed on. It was clear, and at times the snowy Sierra showed dimly in the distance on the east, while Mount Diablo and its range towered grandly on the west.
But this plain is the great feature. The mountains are so dim in the east that they are not conspicuous, so that the plain seems as interminable as the ocean, except on the west. The ground is already dry, the grass very scanty and seldom over two or three inches high. As it grew hotter a mirage flitted around us—a great lake of clear water continually before us for hours. Once the appearance was so deceptive that we took the wrong road, supposing that it led around the water we thought was ahead of us. It took us out of the way, so that we did not strike the right road for some miles. You can have no idea of this extraordinary optical and atmospheric phenomenon. The eye is so deceived that the understanding refuses to dissent from the apparent truth.