36 GEOLOGY AND GOLD DEPOSITS OF THE CRIPPLE CREEK DISTRICT. 
connected; in others they appear to be entirely separate. The basic dikes decom¬ 
pose readily and are not well exposed except in the mines. Though many of them 
have no known connection with ore deposits, others, such as the Elkton-Raven, 
Conundrum, Strong, Anna Lee, North Star, Dolly arden, Pinto, and Block 8 
dikes either contain ore or are closely associated with ore bodies in other rocks. 
TOPOGRAPHIC DEVELOPMENT. 
INTRODUCTION. 
Erosion in its various forms is at the present time the only agent of importance 
that is shaping the topography of this district by sculpturing its surface. But 
during past times constructive as well as destructive forces were at work, and 
during the epoch of eruptions the former were of sufficient intensity to over¬ 
come the work of the latter by building mountains of tuffs and ashes and lavas, 
which erosion again is in a fair way to obliterate. It is difficult to trace the 
physiographic history of a small district without going beyond its borders, and yet 
a little light may be thrown on the subject by a study of the surface forms near 
Cripple Creek. 
In attempting to trace the topographic development we shall find it impossible 
to go further back than to the time just antedating the volcanic eruptions, that is, 
the middle or end of the Tertiary age. The inquiry resolves itself into three parts: 
(1) What were the surface forms previous to the volcanic eruptions? (2) What 
were the surface forms at the close of the volcanic epoch? (3) What changes have 
been effected since that time? 
PREVOLCANIC CONDITIONS. 
Broadly regarded, the region is an undulating plateau, a truncated upland 
with elevations of from 9,000 to 10,000 feet, above which some points rise to indi¬ 
vidual prominence. This plateau is deeply scarred by the abrupt canyons of Oil 
and Beaver creeks, which drain southward into Arkansas River.® In the local 
area this plateau finds expression in the rolling hills southwest of Cripple Creek and 
in Beaver Park in the northeast corner. The individual hills rising above this are 
represented by Trachyte, Rhyolite, and Big Bull mountains, and the volcanic 
complex of hills clustering about Bull Hill. The incised canyons are represented 
by Wilson Creek, Cripple Creek, and Spring Creek. If it were always possible 
to distinguish between intrusive and effusive igneous contacts the task of mentally 
restoring the prevolcanic surface would be much easier. No decisive evidence 
regarding this surface is offered by the whole southwestern contact line of breccia 
and granite. But on Big Bull Mountain, along Grassy Creek, and on parts of 
Carbonate and Mineral hills, as well as on Copper Mountain, there is some good 
evidence that the breccia rests in general on an old surface of granite and other 
rocks. It is inferred with some certainty that Big Bull Mountain existed as a 
rather prominent point in prevolcanic times, and that undulating hills along the 
north side of Grassy Creek and the summits of Tenderfoot and Carbonate hills 
formed part of this prevolcanic surface. The points mentioned belong to the 
a See Geologic Atlas U. S., folio 7 (Pikes Peak), U. S. G • i. Survey, 1894. 
