GEOLOGY OF PAJARO VALLEY. 
37 
hills on the northwest were 1,500 feet high near their termination, while the Llomas Muertas 
were not more than 300 feet high. At the junction of the Arroyo Pescadero with the Pajaro 
diallage hornblende rock is exposed ; this is a spur thrown off from the Gravilan with a strike 
north a little east; west of this, on the right hank of the Pajaro, a stratum of limestone, meta- 
morphic, and about thirty feet in thickness, is exposed; it is a hard, dark, flinty rock, without 
any fossils apparent. From the low hills described, the fossil Venus Pajaroana, (Conrad,) a 
Miocene fossil, was obtained. As the beds containing Dosinia , which, are found so plentifully 
on the Salinas, were not observed here in relation with this fossiliferous bed, it is impossible to 
connect the order of position. 
Leaving the Santa Clara valley, the Arroyo Bonito was crossed before entering the valley of 
San Juan. This stream flows through a small valley bounded on the north by the termination 
of the trachytic range, which formed the east side of the Santa Clara valley, and on the south 
by the low hills alluded to, which approach the river from each side, forming small but beautiful 
valleys, which are terraced on both banks. That on the right or east bank is somewhat higher 
than the opposite one; both extend along the river for eight miles, or so far as the valleys were 
examined, and at the point where the river was first touched the height of the terrace was forty 
feet; a few miles further up it did not appear to be more than twenty feet, the river having 
worn its valley down at the lower end ; the upper surface of the terraces were smooth, with a 
few drift pebbles on the surface, but no beds of sand or apparent shore action. 
