FORMATIONS OF THE NACIMIENTO GROUP 705 



and the walls almost perpendicular. They are composed at the "puerta," or 

 entrance, of a moderately hard, reddish-brown sandstone. The canon is twenty 

 miles in length, its bottom has a gentle rise; and as the sandstone has a gentle 

 dip toward the west as well as south, its upper beds reach the level of the bottom 

 at about the middle of the length of the canon. Above them softer beds [Wasatch] 

 appear, alternating with strata of sandstone; the beds are first gray, but others 

 soon appear which are striped with red. The red-striped marls increase in 

 relative thickness toward the west, and the sandstone strata diminish until at 

 the head of the canon the high lands fall off in masses of hills of bright-colored 

 marls eroded into rounded and picturesquely formed hills. These extend in a 

 long hne to the north and the south, facing westward. To the west, a wide, ele- 

 vated plain spread before us, varied with a few hills, and stretching away with a 

 gentle slope to Canon Largo and the country of the San Juan River. The dis- 

 covery of the variegated marls was one of no little interest to the writer, inasmuch 

 as I had made special efforts to find Eocene beds in this region, and they were 

 now crowned with success. The position of these marls, with their close physical 

 resemblance to the Wasatch beds of Bear River, Wyoming, together with the 

 evidence furnished by a lower molar of Bathmodon, discovered by my guide, 

 indicated that I had discovered the sediments of the great body of fresh water 

 which during successive stages of the Eocene period occupied the drainage-basin 

 of the Great Western Colorado. The thickness of the strata exhibited in the 

 walls of the Canon cita de las Vegas, I estimated at 1,200 feet. 



On leaving the mouth of this canon, and proceeding southward, the southern 

 dip of the red sandstones [Wasatch] brings their summit to the ground-level in 

 about ten miles' distance. The red and gray marls with alternating beds of 

 white and yellowish sandstone [Wasatch] appear on their summits, and at a 

 point twenty miles south of the canon, form a mass of badland bluffs of from 

 600 to 1,000 feet elevation. This escarpment retreats and then turns to the east, 

 forming an extensive horseshoe, the circumscribed area being occupied with 

 hills and picturesque masses of sediment, with all the pecuhar forms and desola- 

 tion of badland scenery. I remained in camp for about a month near this circle, 

 and obtained many fossil remains of vertebrates [Wasatch]. Ten miles south of 

 this point another horseshoe of badlands covers an extensive area, and proved 

 to be as rich in fossil remains [Wasatch] as the first. Here I made my second 

 camp, remaining in it for three weeks. The southern boundary of the northern 

 tract extends to within six miles of the Cretaceous hog-backs, while the corre- 

 sponding part of the second approaches nearer, forming a line of bluffs of con- 

 siderable height running north and south parallel with, and half a mile from, the 

 hog-backs. Beyond the Puerco divide, hills of this formation rise on both sides 

 of the trail, and near the Ojo de San Jose, the Eocene beds repose on the foot 

 of the Nacimiento Mountains several miles to the east. 



Below the sandstones which form the portals of the Canoncita de las Vegas, 

 another stratum of marls [Puerco] shows itself in hills of 100 feet and higher, in 

 the sage-brush plain that separates them from the Cretaceous hog-backs. They 



