Page:The American Cyclopædia (1879) Volume XIV.djvu/393

 ROCKY MOUNTAINS 377 ley of Roches Moutonns creek, which flows into Eagle river from its N. E. base, are very remarkable rounded masses of granite, such as have long been called sheep backs or roches moutonnes in the glacial regions of central Eu- rope. Here they are shown on a grand scale. In the valley of the Arkansas and the Gun- nison are marvellous examples of lateral and terminal moraines, and there are numerous lakes whose basins have been scooped out by some extended glacial action. The Twin lakes are beautiful sheets of water on the E. side of the Sahwatch range, 2 to 3 in. in diameter and about 80 ft. deep. These are true glacial lakes. The proofs of glacial action are com- mon throughout the Rocky mountain region, but they are nowhere shown to such a marked extent E. of the Sierra Nevada as in the vicinity of the Sahwatch range. From the W. side of this range flow the Gunnison river and southern branches of the Grand, which, after cutting deep canons or gorges, unite near the western boundary of Colorado ; and cutting a still deeper cafion, the stream flows into the great Colorado of the West. West of the Sahwatch or great "Mother" (Madre) range is another remarkable group in the drainage that leads to the great Colorado, called the Elk range. It is about 50 m. in length, with a trend about N. W. and S. E., and differs from any of the others mentioned both in form and structure. In this range are seven peaks of the first order, rising to an elevation of nearly 14,000 ft., and many others ranging from 12,000 to 13,000 ft. The geolo- gical structure is very peculiar. It appears that the vast thickness of sedimentary strata once rested upon a floor of igneous granite in a pasty or semi-pasty condition, and that these high peaks were thrust up through the overlying beds, in many instances completely overturn- ing them for miles in extent. There are faults 2,000 ft. in extent, and dikes without number, where the igneous material seems to have been squeezed through fissures in the thousands of feet of overlying strata, vertically as well as horizontally. Deep gorges and amphitheatres meet the eye on every side. Snow Mass peak, 13,961 ft. high, is so called from the immense mass of perpetual snow on its sides. At its immediate base, on all sides, are beautiful lakes. The surface is remarkably rugged, an,d as far as the eye can reach on every side are high peaks with deep gorges in one continuous suc- cession, while the sedimentary rocks are thrown into chaos. On the N. W. end of the range is a remarkable peak which forms an excellent landmark, known among the miners and pros- pectors for years as Sopris peak, 12,972 ft. high. From this point the land slopes off into the remarkable plateau country bordering on the Colorado river, literally gashed as it were by the little streams which have cut innumera- ble canons through it. There is probably no country in the world that presents more ob- struction to the traveller. At first glance the Park range appears to be connected with the Sangre de Oristo range, which bounds the E. side of the San Luis valley, but the former is separated from the latter by the Arkansas val- ley, and really lies parallel with it. It begins in lat. 38 26', Ion. 106, trends S. 30 E., and shows on its summit a continuous series of sharp peaks. Parallel to it, on the east and bordering the plains, is the Wet mountain range. The interval is known as the Wet mountain valley and Huerfano park, one of the most beautiful and fertile districts in Colo- rado. These mountains extend far down into New Mexico. Southward the Sierra Blanca and Spanish peaks are lofty landmarks. Fort Garland, an old military post in the San Luis valley, is near the base of the Sierra Blanca. The San Luis valley, though nearly surrounded with high ranges, is not a park, but a valley 30 to 50 m. wide, through which the Rio Grande flows after emerging from the San Juan mountains, cutting a gorge through its basaltic floor 1,000 to 1,500 ft. in depth for 60 to 80 m. Immediately W. of the upper portion of the San Luis valley, in S. W. Colo- rado, is a most interesting as well as lofty group of mountains, forming what is now called the San Juan district. These moun- tains form the sources of a great number of streams. On the north are many branches of the Gunnison, on the east the Rio Grande, and on the south and west the various branch- es of the Rio San Juan, which flows S. W. and W. and unites with the Colorado. Within an area of about 4,000 sq. m. is the most im- portant and rugged group of peaks in Colo- rado, and probably in the first division of the Rocky chain. More than 100 points are above 13,000 ft., and about 10 peaks over 14,000 ft. On the N. side of the group is the lofty Un- compahgre or Uncapahgri peak, with its dome- shaped summit rising to a height of 14,235 ft. Large areas here are composed entirely of quartzites, and others wholly of igneous rocks. Toward the south, in southern Colorado and in New Mexico and Arizona, the volcanic ac- tion seems to have been very great, and the area covered with igneous rocks increases ; sometimes they occupy several thousand square miles, to the exclusion of all others. What are called the broad table lands or mesas of New Mexico are simply floors of basalt. Colorado may be regarded as the culminating area of lofty points in the eastern division of the Rocky chain, as California is in the western, in its Sierra Nevada ranges. Within the limits of Colorado are 50 or more points exceeding 14,000 ft. in height, and more than 250 of over 13,000 ft., while the number reaching 12,000 ft. is unknown. The average elevation of Colorado is greater than that of any other state or territory in the Union, being 6,600 ft., while California with its magnificent group of peaks in the Sierra Nevada averages only 2,800 ft. To the west, and walling in the great in- terior basin on the east, is the Wahsatch range,