TO JUNCTION OF GRAND AND GREEN RIVERS, 109 



and along the margin of the streams groves of cottonwood, and thickets of willow and 

 buffalo-berry (Elcaijnus argenteus?}. 



Though now entirely deserted, these valleys were once occupied by a dense pop- 

 ulation, as is shown by the extensive ruins with which they are thickly set. Those on 

 the Animus, twenty miles above its mouth, have already been noticed. 



At the junction of this stream with the San Juan the remains of a large, but very 

 ancient, town are visible, the foundations of many buildings of considerable size still 

 remaining, and traces of an acequia through which water was brought from a point some 

 miles above on the Animas. 



Near Camp 43 also are the ruins of several large structures, of which portions of 

 the walls of stone are still standing, twenty or more feet in height. Indeed, it may be 

 said that from the time we struck the San Juan we were never out of sight of ruins, 

 while we were following up its valley. 



CANON LARGO. 



At Camp 44 we left the valley of the San Juan and entered the mouth of Canon 

 Largo, which we followed up in an easterly direction until, at its head, near the western 

 base of the Nacimiento Mountain, we came out on to the surface of the great plateau 

 of the Upper San Juan, through which we had been so long passing, sunk far below 

 its surface in the excavated valleys which intersect it. Of these valleys Canon Largo 

 may be taken as a type. It differs in nothing from that of the San Juan or Animas, 

 except that, instead of a large perennial stream, a small, generally dry, arroyo traverses 

 its bottom, and its boiinding cliffs, composed of the upper strata of the table-lands, 

 exhibit geological features not met with in other portions of our route. 



By the easterly dip of the rocks and the rapidity of the fall of the stream, we were 

 constantly ascending in the series from the Creston to the head of Canon Largo. At 

 the moiith of the Animas we had nearly sunk the whole of the Middle Cretaceous group, 

 its upper members (gray shales and marls) forming the base of the high cliffs, composed 

 mainly of the Upper Cretaceous sandstones, here very massive, and showing- a thick- 

 ness of 600 to 700 feet. At the mouth of Canon Largo we had risen still higher in the 

 series, the Middle Cretaceous shales having entirely disappeared; the lofty cliffs which 

 bound the valley at this point being formed entirely of the Upper Cretaceous rocks, 

 alternations of soft yellow sandstones and white, gray, or purple marls. The lowest 

 member of this series here is the same with that which forms the summit of the Creston 

 section, and more fully exposed at the mouth of the Animas, where it presents perpen- 

 dicular faces of 300 to 400 feet of massive, homogeneous, soft, yellow, calcareous sand- 

 stone. A few miles farther north, on the La Plata, this rock contains at its base Am- 

 inonitcs placenta, Baculites ovatus, &c., Avhich serve to mark very satisfactorily its place 

 in the geological scale, viz: Upper Cretaceous, No. IV or V, of Meek and Hayden's 

 Nebraska section. This is surmounted by some ten alternations of marls and sand- 

 stones in the cliffs bordering Canon Largo, the series being entirely conformable and 

 similar in lithological character throughout. At the head of Canon Largo, as we shall 

 see further on, these strata are succeeded by others, several hundred feet in thickness, 

 also conformable, but, lithologically, showing a preponderance of marls over the sand- 



