PREFACE.

THE object of this report is to present, in a concise manner, a sketch of the Geological Structure, Industrial and Economic Resources of the State, included in the above section named, and which comprises the Mineral Districts proper, as understood at the present time, and includes portions of the eastern valleys of the Sacramento and San Joaquin, and to the coast line within the 41st and 42d degrees of north latitude.

Personal observations were made during the autumn and winter of '50 and '51, and also of '52, and the entire line of travel was conducted for the most part on foot, for the better purpose of more critical examination.

Persons unfamiliar with the modifying circumstances affecting the general characters and positions of rocks, are apt to be often deceived in their perceptions respecting them, consequently, but little assistance can generally be obtained by inquiry respecting the peculiarities that may be present in

the various formations.

This circumstance is sufficient to show the necessity of personal examination of Districts, in order to deduct legitimate and correct conclusions respecting them; and this course was adopted during the examinations that were made in nearly every case. In the remarks that follow in this report, I shall confine myself for the most part, strictly to the Geology of the District included, alluding to its Geognosy so far only as will be necessarry for an elucidation of the subject that may be under consideration.

Researches on the eastern slope of the Rocky Mountain chain will prove of little avail in this State, as we cannot form an opinion from the presentations there made in the various and similar formations of that chain, and more especially, when we find that these similar formations are commingled, disturbed, and changed, by rocks of widely different character and compo

sition.

The necessity then, of studying closely each different group, will become apparent, and at the same time more complex and difficult.

GEOLOGY

OF THE

SIERRA NEVADA, OR CALIFORNIA RANGE.

*

THE largest portion of the State of California, is comprised between the summits of two distinct ranges of Mountains, denominated the Sierra Nevada, or California Range of the Cascades, and the Coast Range on the west, the more central portion is an extensive valley through which flows the two principal rivers of the country, the Sacramento and San Joaquin.

The equivalents of the California Range to the north, are the Cascades extending into Oregon; and its principal lateral spurs, as it approximates the parallel of 42d north latitude, is found in the Siskiyou Range, which separates from the Cascades at nearly a right angle near the line of 42° 20', and pursues a tortuous course to within some eight miles of the coast, in about latitude 41° 40′ north, at which point it becomes completely merged in the coast line of mountains.

This spur forms the northern boundary of the Klamath river, as also a large portion of the northern boundary of the State; and which, with its lateral spurs, forms an interesting and important feature of this portion of the country.

The principal latteral spur of this range is given off near the line of 122° 50' west longitude, and pursues a southwest course for sixty or seventy miles, and unites with a similar spur some eight or ten miles south of Mt. Shasta, which has its intersection with the main Siskiyou Mountains in longitude near 123° west; the Klamath river cuts these two spurs near both of the points designated. Within the triangular space formed by this junction, are extensive valleys, as the Scott and Shasta illustrate.

The Siskiyou range will maintain an average elevation nearly equivalent

* Sierra Nevada is inappropriate, according to Lieut. Wilkes' U. S. Ex. Ex., as it blends the principal with part of another.

to the Cascade range for a large portion of its course, and an elevation superior by at least one-third to the Sierra Nevada, within the same parallel. The highest portion of the range being found in Mount Shasta and Mount Read, within fifty miles of the coast.

These mountains partake, in a great measure, of the general characteristics of the Sierra, but in some points they vary in a material degree. In this particular, they become the more interesting, from the variability of the mineral characteristics which they present, and the prospective of other sources of wealth and economy which no part of the western flank of the Sierra presents. And allusion will be made to these points under their appropriate heads.

Mr. Tyson, in speaking of the California Range, very properly remarks, that "in Geological structure the Sierra Nevada resembles the Andes," and the analogy also holds good in being like the Andes, one great ridge, instead of a chain of ridges, such as constitute the Appalachian Range, and it is to this chain on the Pacific that we can look with any hope of success to the development of that article of great economic value, so necessary to the convenience and necessities of the growing wants of our State-mineral coal.

The altitude of the Sierra has been variously estimated, but its average height is probably within six thousand feet; while the coast range proper will not attain an altitude that will much exceed three thousand feet throughout its extent.

The formations which compose, for the most part, the western flank of the Sierra, are hypogene (volcanic) and metamorphic (changed) rocks; as these make up the greater part of the range, it must not be inferred (as has been done) that, from their similarity of composition, that their upheaval was simultaneous, for the strongest evidences exist that it was far otherwise. In this, as in all other volcanic districts, there was undoubtedly long periods of quiescence or a state, to say the least, that was comparatively quiet, occupying long intervals between the disturbing forces that were instrumental in developing this portion of the continent. The time that elapsed during the successive periods of elevation which have occurred, is beyond our utmost conception, and we arrive at the fact only through the medium of analogy.

But although there are periods in our geological history that exceed our utmost comprehension, still there are some evidences that disturbances have occurred at a comparatively recent date, even perhaps during the historic period: but this subject will again be alluded to in the sequel.

The characteristics of the volcanic rocks of our mountains are in most cases very uniform, but where discrepant features do arise in the hypogene or metamorphic rocks, it will often be found that local circumstances have exerted a great influence often in those modifications.

In illustration of this we will cite an instance. It is well known that talcose rocks form a large proportion of the aggregate of the plutonic series of this State. They are found in close proximity with the primary calcareous formation in many cases; in other instances, miles distant from the calcareous rocks.

It is a well known fact that intrusive dikes of trap, in passing through limestone, will change the calcareous formation to true talcose rocks ;* and

* McCulloch.