SCENERY. 87 
far distant as to be below the horizon, are made to rise into 
view in distorted and changing outlines. Inverted images of 
smaller objects, and apparent lakes of clear water, are often 
seen, and invite the traveller to turn aside for refreshment. 
The first exhibition of mirage that was seen [by Blake’s party] 
was from the margin of the plain at Carriso Creek, looking 
toward the Gila, about ninety miles distant. It was early in 
the morning, and the eastern sky had that golden hue which 
precedes the rising sun. Tall blue columns, and the spires of 
churches, and overhanging precipices, seemed to stand upon 
the verge of the plain. Their outlines were changing gradu- 
ally, and, as the sun rose higher, they were slowly dissipated. 
After reaching Fort Yuma, and witnessing the strangely pre- 
cipitous and pinnacled outline of the mountains beyond, it was 
at once apparent that the mirage consisted of their distorted 
images. When we were upon the northern part of the desert, 
the peak of Signal Mountain was often distorted and raised 
above the horizon. The points of distant ranges also seemed 
at times to be elevated above the surface, precisely as the 
headlands of a coast sometimes appear to rise above the water 
at sea. 
“Many of the phenomena called mirage are not due to re- 
fraction, but are believed to be the result of reflection from 
the sand, or smooth surface of clay, or the polished pebbles. 
The smooth clay forms an excellent reflector for all the rays 
which are incident at a slight angle, and is most frequently 
the cause of the appearance of water. The beautiful surface 
of the pebbly plain may be regarded as a combination of myr- 
iads of reflectors; for each pebble is so highly polished, that it 
reflects light almost like a mirror. The reflection from such a 
brilliant surface, when seen at a favorable angle, looks like a 
sheet of water, the similarity being heightened by the motion 
of the stratum of heated air in contact with the surface.” 
The phenomena of mirage are frequently witnessed in the 
Sacramento Basin, and also in the coast valleys, on warm, dry 
days. 
