CHAPTER V. 
SANTA MARGARITA VALLEY. 
Extent and limits of the valley.—Its beauty and fertility.—Geological structure.—Character of the granite.—Disturbed 
rocks.—Trap protrusions.—Stratified rocks of the valley.—Order of position and nature of the beds.—Nature of the 
fossils included—Relative position of the fossils in four beds.—Relation opposition of the beds of this valley with 
THOSE IN THE SALINAS VALLEY.—SUMMARY OF THE OBSERVATIONS ON THE VALLEY. 
The valley of Santa Margarita, in San Luis Obispo county, comprises the sources of the Salinas 
river. It is a small plain, whose greatest breadth is nine miles, narrowed towards its southern 
end to a width of three miles by upheaval of low hills; it lies between the valley of San Luis 
Obispo on the west and the valley of the Estrella or San Juan river on the east, and may be 
looked upon as the southern prolongation of the Salinas valley, from which it is separated by the 
low hills south of San Miguel. Its eastern boundary is the prolongation of the Point Pinos range 
of hills, which have been described as running southeast from Monterey, and which, fifty miles 
south of that city, become less elevated and more spread out; in their southerly course they 
cross the Salinas river, and iij its upper portion become the eastern boundary, as they were its 
western lower down ; along this valley they are low mountains, not more than 1,000 to 1,200 
feet above the level of the plain, itself 950 feet above the sea ; further south these hills rise 
to a considerable height, are more pronounced, and known then as the San Jose mountains. 
The western boundary of the plain is another of the coast ranges ; the Santa Lucia hills, one 
of the longest and most decided of the coast ranges, with few breaks or passes in it, and rising 
to a height of 2,500 feet. The valley between these limits is one of the most beautiful and 
fertile in south California, possessing fine grass, with abundance of running streams in the 
bottom, the side hills clothed with live oaks and cotton-wood, and covered with a luxuriant crop 
of wild oats, (avena fatua,) which was naturally preserved, and at the time of visit, (January,) 
served aS food for the multitude of deer and horned cattle, which found abundant sustenance 
here. The oak trees are covered, as to their branches, with the beautiful ramalina, which, 
hanging gracefully in festoons, with its light green tint, convey the idea of spring at a season 
when vegetable growth is nearly suspended. The Salinas river flows upon the east side of this 
valley, from the level plain of which it is separated by a range of low hills of sandstone grits ; 
beyond (east of) the river the granitic axis of this range appears, having the same mineral consti¬ 
tution as further north, largely felspathic, with well defined orthose crystals, of a light flesh 
color, vitreous quartz, and small plates of diallage, whose green tint adds a lively contrast to 
the felspar, and gives an appearance of syenite to the whole mass ; the rock is cut through by 
thin green threads of oxide of chrome, along the line of which the mass breaks into small 
rhombic fragments. It is a granite which decays readily from the separation of the felspar 
crystal, which drops out by the weathering of the paste. 
At the southern end of this valley the granite becomes highly magnesian from the intermix¬ 
ture of serpentine protrusions. These are derived from the Santa Lucia, whose axis is serpen- 
