246 GUIDEBOOK OF THE WESTERN UNITED STATES 
ing the gold rush of 1849 a stone structure called Fort Defiance was 
built by Americans in connection with a ferry across the river near by. 
It was soon abandoned after a massacre by the Yuma Indians. 
As the level of the general desert plain is attained near Knob siding 
many prominent mountains come into view—the rough ridges of the 
Cargo Muchacho Mountains near by to the north, a 
group of high ridges surrounding the sharp Picacho 
Peak to the northeast, and various high ranges back in 
Arizona. Some of these mountains consist in whole 
or in part of volcanic rocks; others are made up of 
old gneisses and granites, such as constitute the Gila Mountains. A 
group of rocky knobs of vesicular lava, skirted 2 miles southeast of 
Ogilby siding, has been a source of railroad ballast. On approaching 
Ogilby the Cargo Muchacho Mountains seem near. They consist of 
schists and include a number of mines, old and new. The principal 
old one, the American mine, was worked from 1879 to 1918, with a 
production locally estimated at several million dollars. Near by are 
the ruins of Tumco (formerly Hedges), a town which had a popula- 
tion of nearly 1,000 when the mines were operating. The ore was in 
veins in pegmatite, which cuts the schist in every direction. 
Three miles north of Ogilby is a mine producing cyanite, a very 
refractory aluminum silicate that is useful in the manufacture of high- 
grade porcelain ware, electrical insulators, and refractory brick and 
shapes for the glass and iron industries. This mineral, which is of a 
beautiful blue color, occurs in a large vein with quartz, in mica schist. 
It is shipped to Los Angeles for the separation of the quartz and 
preparation for the market.” A mile north of the cyanite mine talc 
is mined, for use largely in paper manufacture. 
West of Knob siding and extending from the Mexican boundary to 
and beyond Amos siding, a distance of 50 miles, is a wide belt of sand 
hills which is more familiar to most persons than they are aware, for 
it has afforded the background for many ‘‘Sahara Desert”’ scenes in 
the moving pictures. The belt is about 5 miles wide. It presents a 
picturesque succession of shifting dunes, of loose pale-yellow sand, in 
places 200 to 300 feet high, separated by irregular basins. The high- 
way to El Centro formerly passed over this sandy strip on a road 
made of heavy planks strung together with wire. It was 10 feet wide, 
with passing places at intervals. In 1928 this unique roadway was 
displaced by a wide concrete highway suitable for the present heavy 
” Cyanite is of the same composi- 
Ogilby. 
Elevation 356 feet 
New Orleans 1 
miles 
fibrous cyanite from the quartz is 
ted 
_ silica 37.15 per cent, the proportion of 
alumina being considerably greater 
_ than in clay. The separation of the 
water, which shatters the quartz so 
that it can be removed by washing and 
