352 The American Geologist. Sune, aoe 
crystalline and Tertiary rocks at this locality is a faulted one, 
producing the effect of overlap. Certain black, very basic 
gabbro dikes in the neighboring gneiss may represent the 
roots of the volcano. There are no evidences of a crater as 
the old voleano has been turned up on its side and deeply 
eroded. 
The Tertiary formations in this region have the struc- 
ture of a trough trending northeast to southwest and closed 
on the northwest end. They dip toward the axis of the trough 
and curve around the northeast end-in a very beautiful and 
instructive manner. Each successive series laps past the next 
older, so that the older series are in the forms of crescent or 
horse-shoe-shaped areas, having their greatest width at the 
northeastern end of the trough and rapidly thinning out and 
disappearing on its sides. 
The Escondido series appears first at Mint canyon, several 
miles west of Tick canyon, and trends eastward, widening to a 
maximum of about one mile, a little east of the latter canyon. 
Just east of the valley of the Aguadulce creek, where is the pro- 
longation of the axis of the trough, the sandstone swings rap- 
idly to the south, but the line of lava peaks continues eastward. 
The lava range doubtlessly marks the site of a set of east-west 
fissures. Perhaps it was the outflow of lava through these 
fissures that caused a subsidence of the region and permitted 
the accumulation of several thousand feet of sediments over 
what had just previously been a land area. 
The Escondido canyon, the next main valley east of the 
Aguadulce (the latter marked on some maps as the Canyada de 
la Sierra Pelona,) exposes a splendid section through the series. 
The following thicknesses are merely estimates. The series of 
lavas and sandstones dip westerly at angles of 20° to 40°, 
the prevailing dip being 30°. The exposure is so perfect in 
the narrow winding canyon with precipitous and even over- 
hanging walls that no faulting can have escaped attention. 
seginning at the head of the canyon there is, resting on the 
schist-gneiss-granite-complex— 
Section in Escondido Canyon Thickness. 
1. A coarse breccia-conglomerate of angular and subang- 
ular blocks of granite, gneiss, etc., from the underly- 
ing older complex, all well cemented and in places 
clearly ystratifiied 334.5 fn eek ee ee cee coo feet. 
