738 JOHN W. GRUNER 



Distribution of the sediments. — -The sedimentary rocks cover 

 portions of the Pueblo Creek and Red River drainage basins, and 

 extend far beyond the southern and eastern margins of the area 

 mapped. While the thickness of the formations may be estimated 

 at several thousand feet, at least 2,500 feet in the southeast corner 

 of the district, erosion has reduced the thickness of the sediments 

 toward the northwest to less than 300 feet above Sacred Lake. 



The contact of the sediments with the pre-Cambrian rocks follows 

 approximately a line from the southwest corner of the quadrangle 

 to a point on Starvation Creek, about i mile south of Pueblo Peak. 

 A normal fault of unknown displacement, probably relatively small, 

 has sharply upturned the sandstones and limestones against quartz- 

 chlorite schists west of Starvation Creek. Here at the bottom of 

 the creek ioo=t feet of dense gray non-fossiliferous limestone are 

 seen the base of which is not exposed. On it rests a dense, brownish- 

 gray, arkosic sandstone that is brownish red when weathered. This 

 rock caps most of the ridges and is of great thickness. 



Farther east, on the high divide between Pueblo Creek and 

 Lucero Creek, the foregoing limestone is overlain by a greenish- 

 gray calcareous and arkosic grit. This grit is of wide extent and 

 great thickness, not only in this district, but beyond its limits. At 

 certain horizons this rock is replete with fossil fragments, especially 

 crinoid stems. It becomes gradually coarser toward the top of the 

 formation and changes to a conglomerate which contains subangular 

 pebbles of quartz, gneiss, granite, and schist. They do not exceed 

 a diameter of i inch, but attain greater dimensions on Burned 

 Ridge. 



About i§ miles south of Larkspur Point, where the strata rest 

 on pink granite, the beds dip steeply soutwestward. The basal 

 conglomerate clearly derived from the pre-Cambrian rocks beneath 

 grades into sandstones, grits, and conglomerates. They are of 

 great thickness and constitute no definite, sharply separated mem- 

 bers. The attitude of the beds in connection with the dip of the 

 same formation in the opposite direction on the southwest slope of 

 Burned Ridge, near a point where a fault crosses Meyer's Creek, 

 indicates a synclinal structure whose axis runs at right angles to 

 Burned Ridge and pitches southeast. 



