GEOLOGY — GENERAL FEATURES OF SACRAMENTO VALLEY. 21 



interspersed with a great variety of flowering annuals, while the gravelly and more unproduc- 

 tive portions support a thinner growth of coarser plants, (Eryngium, Hemitonia, Maddria, &c.) 

 Of trees, there are none, except such as grow in narrow lines along the streams. These helts of 

 timber are of varying breadth, from a mile or more, of wide-spreading magnificent oaks, 

 (generally Quercus Hindsii,) to a meager border of willows, poplar, or sycamore, hung with 

 festoons of grape along the water's edge. 



Bordering the central plain on either side is a second "bench," or terrace, generally less than 

 100 feet above the lower, and which sometimes, by erosion, thrown into low rounded hills, 

 oftener forms a distinct prairie plain. Crossing this upper terrace toward the mountains we 

 soon rise into the foot hills, which are covered with groves and clumps of oak, with here and 

 there scattered trees of the nut-pine. The scenery of the foot hills is frequently picturesque 

 and beautiful, with its lawn-like slopes and clumps of spreading oaks, presenting views which 

 might well serve as models for the landscape gardener. 



The agricultural capabilities of the different parts of the Sacramento valley, though consid- 

 erably influenced by the structure and constituents of the soil, are more directly dependent on 

 the degree in which its greatest want — the want of water — is supplied. With an abundance of 

 this indispensable element, it would be one of the most productive portions of the globe. 



COAST MOUNTAINS. 



The structure of the coast mountains, where they form the western border of the Sacra- 

 mento valley, is apparently similar to that of the same ranges in the vicinity of San Fran- 

 cisco, which has already been described. They form a belt thirty to fifty miles wide, 

 composed of several associated ranges, and having an altitude of from 3,000 to 5,000 feet. 

 They are composed, for the most part, of volcanic rocks, trap, trachyte, pumice, with occasional 

 protrusions of granite and serpentine. The flanks of these mountain ranges on either side are 

 interruptedly occupied by tertiary sandstones, and by volcanic marls and tufas of still more 

 recent date — the sandstones containing characteristic Miocene fossils; the finer marls containing 

 infusoria, generally of fresh water origin. 



Near Tomales bay a bed of whitish limestone occurs, highly metamorphosed, exhibiting no 

 fossils, and as yet of unascertained age. Specimens of a limestone containing no fossils were 

 also collected by Lieutenant Abbot near Yreka. There are in many localities on the coast 

 mountains, particularly near the north end of the Sacramento valley, metamorphic slates, some- 

 times auriferous, which are probably of ancient date ; but this is only conjecture, as they have, so 

 far, yielded no fossils. 



SIERRA NEVADA. 



The structure of the eastern wall of the valley of the Sacramento has not yet been fully 

 made out. It is, for the most part, composed of the same geological constituents as the 

 coast mountains, having an origin due to the same general system of elevation, and probably 

 nearly the same date, i. e., subsequent to the deposition of some of the tertiary strata. 

 I should, however, be disposed tojegard the Sierra Nevada as having had an existence, and the 

 greater part of the range as having been above the level of the ocean previous to the deposition 

 of the San Francisco sandstone, which is so characteristic of the coast mountains, and which, 

 if it can be identified in the Sierra Nevada, is probably confined to its flanks, at a low level. 



A metamorphic limestone is found at intervals throughout all that part of the Sierra Nevada 

 which skirt the California valley. Its age has not been determined, as it is generally highly 



