HUNTINGTON AND GOLDTHWAIT: THE HURRICANE FAULT. 237 
still mature so far as the St. George block is concerned. Here and there, 
however, are evident indications of renewal, such as a shallow canyon cut 
through a lava flow, or thé shallow valleys which all the streams have 
cut in the heavy gravel deposits which fill the bottom of the wash and 
therefore belong to a time anterior to the last great faulting. Thirty 
miles farther southwest — that is, about one hundred miles southwest of 
Toquerville — at Scanlon’s, or, as it is now called, Gregg’s ferry, fifteen 
miles below the mouth of the Grand canyon, the same feature is seen. 
The Colorado river has intrenched itself to a depth of about two hundred 
feet in heavy gravels which at an earlier time must have filled its broad 
valley to a considerable depth. The extensive valley floors, grade plains, 
and the other forms of mature topography west of the Hurricane all 
seem to indicate that at the end of the inter-fault cycle the topography 
of the St. George block was of the same type as that which we have 
already described from smaller samples preserved in the uplifted block 
east of the Hurricane. In both blocks there has been a renewal of 
erosion, although it is much more marked in the eastern block. The 
connection between these renewals will be considered later. 
Summary. All the lines of evidence which we have been pursuing 
lead to the same conclusion. The unequal recession of cliffs on the two 
sides of the Hurricane fault; the bits of ancient surface preserved 
under lava flows ; the mature topography of the Colob plateau ; the con- 
trast between the old and new faults at Kanarra, and the grade plains, 
mature topography, and broad surfaces covered with gravels west of the 
Hurricane — all point to a long period of quiet erosion between the first 
and second faultings. At the end of this inter-fault cycle of erosion the 
whole country was physiographically mature or even old. Certain 
regions of soft strata, chiefly near the Colorado river, had been reduced 
very nearly to base-level forming the Mohave peneplain. 
Attitude of the Land, and Topography at the End of the 
Inter-Fault Cycle. 
In our study of the borderland between the Plateau and Basin Range 
provinces we have already found two critical points, and now have come 
to a third. The first was at the end of the long cycle of deposition 
just before the strata were upheaved, flexed, and folded; the second 
was at the end of the time of quiet, when flexing had ceased and the 
earlier faulting had not yet begun; the third is at the end of the in- 
