CHAPTER VII. 
GEOLOGY OF REGION ABOUT SAN FRANCISCO MOUNTAIN. 
GENERAL FEATURES.—RELATIONS OF THE SAN FRANCISCO GROUP TO THE MOGOLLON SYSTE M.—GENERAL ASPECT AND ISOLATED CHARACTER 
MOUNTAIN.—MODERN VOLCANIC PHENOMENA OF ROCKY MOUNTAIN AND PACIFIC REGION.—OSCILLATIONS OF LEVEL AST.— 
EaRrHQuakes.-—ConrTINUED AGITATION OF WESTERN HALF OF THE CONTINENT THROUGH ALL GEOLOGICAL AGES.—LOocCAL GEOLOGY.— 
DRIFT OF VALLEY OF LITTLE COLORADO.—TRAP PLATEAUS WEST OF SAN FRANCISCO MOUNTAI COVERED BY IT.— 
SECTION OF STRATA FROM PICACHO TO BILL WILLIAMS’S MOUNTAIN.—PARTRIDGE AND CEDAR CREEK3.—UPPER CARBONIFEROUS LIME- 
STONE.—CROSS STRATIFIED SANDSTONE.—AGE OF ROCKS DESCRIBED BY MR. MARCOU ON PUEBLO AND CEDAR OREEKS.—+NO DEVONIAN 
OR PERMIAN STRATA IN THIS VICINITY.—BILL WILLIAM:’3 MOUNTAIN, MOUNT KENDRICK AND MOUNT SITGREAVES.—CARBONIFEROUS 
LIMESTONE.—MopEgN VOLCANIC CONES AT CAMP 44,—MAGNESIAN LIMESTONE WE3T OF LITTLE COLORADO.— PROBABLY CARBONIFEROUS. 
GENERAL FEATURES. 
Allusion has so frequently been made to the San Francisco mountain in the preceding pages, 
as well as in the report of Mr. Marcou, (Pacific Railroad Report, vol. III,) that but little now 
remains to be said of it; and yet our exploration of this district was so thorough, and our 
observations have such a bearing on those of the geologist before mentioned, that I have 
thought it desirable to give a brief notice of them. . 
The relations which the San Francisco and adjacent mountains sustain to the chains which 
approach nearest to them are by no means obvious; and it remains yet to be demonstrated 
that this group is not—what at first sight it seems to be—entirely disconnected with any line 
of upheaval. It is probable, however, that some light will be thrown upon this subject by an 
examination of the unexplored region between these mountains and the river Gila. 
Such explorations would also result in a valuable contribution to geological science, by 
giving some intelligible analysis of the structure of the Mogollon mountains in place of the 
theoretical—and, as it seems to me, erroneous—descriptions which have been published of 
them. It is possible, and perhaps probable, that the Mogollon mountains will be found to have 
such a trend and extent as to permit a connexion to be established between them and the San 
Francisco group ; but however this may be, my own convictions, derived from observations— 
partly my own and partly those of others—completely encircling the mount ins in question, 
are entirely opposed to the theory which gives to their axes a nearly east and west trend, and, 
disconnecting them from the ranges of the Rocky mountains and Sierra Nevada, establishes 
upon them a new system of elevation, to which is assigned a distinct and entirely imaginary 
epoch. — 
To the casual observer the San Francisco mountain forms a most impressive feature in the 
scenery which surrounds it, not only from its symmetrical and striking outline but also from 
its isolation. Rising in solitary grandeur to the altitude of 12,000 feet above the sea, its snowy 
summit is visible from nearly all parts of a circle drawn around it with a radius of a hundred 
miles. In all that region it is without a rival or an associate, except its immediate subordi- 
nates ; and in its relief from the table-land on which it rests it may be compared to some rocky 
island rising from the surface of the sea. 
Its geological structure fully accords with its physical aspects. It is volcanic throughout, 
and is, in fact, a huge volcano whose fires have been but recently extinguished. Through one 
great, and several minor vents, opened in the strata of the high mesa, where they have a 
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