They can be defined only as a mass, with a long spur, of magnitude amply sufficient to entitle it to the name of range, running southward, and forming the western wall of the San Luis Valley.

To the

This mass radiates drainage in all directions. east flows the Rio Grande; to the south the Animas, Florida, Pinos, and the main San Juan; to the west and north the Dolores, San Miguel, Uncompahgre, and other large tributaries to the Grand River. Within these mountains there is no level country, practically. The largest valley, known as Baker's Park, is but four miles long by half a mile in width. It is unnecessary to go into details regarding the height of this range. Suffice it to say that it contains at least a dozen peaks exceeding 14,000 feet, and between one and two hundred above 13,000 feet.

South of this group, in New Mexico, the level of the plateaus is broken by several ranges of greater or less magnitude. Among them may be mentioned the Zuni Mountains, whose peaks reach 12,000 feet; the Sierra Magdalena, Sierra Mateo, and the Sierra de las Mimbres.

28. The Continental Divide

The water-parting of the continent is borne throughout by this system of mountains, most of the way following the crests of ranges, but in some cases stepping down to the broad flat surfaces of plateaus.

In the British Possessions we find it first following the crest of the western member of the system, and, as we trace it southward, it is seen to step eastward from range to range, until, on entering the territory of Montana, it is found that the eastern range bears it. At the south end of this range a western offset is made to the Bitter Root Range, which it follows south-eastward to its

end. Then it follows the summit-line of a broken plateau-like country, in which are several excellent passes, to the head of the Wind River Range, whose jagged crest separates the Colorado from the Big Horn. This range,

ending abruptly, leaves only a broad plateau to divide the waters. The Park Range next takes up the "divide,” carrying it to the head of North Park, where it makes a great loop to the eastward to enclose Middle Park in the area of Pacific drainage.

Then it sweeps far to the westward, and follows the high summits of the Sawatch Range to its end; then, pursuing a winding course in the confused mass of the San Juan Mountains, it takes itself again to the plateaus, and follows an ill-defined southerly line to the borders of Mexico. Though it follows, as nearly as can be determined, the summit-line of the great general elevation, it by no means follows that it occupies the crests of the highest ranges in the neighbourhood. The reverse seems to be as frequently the case, that there are, on the right and left, ranges which in altitude may overtop that which separates the streams of the two oceans.

CHAPTER VII.

THE PLATEAU REGION OF THE COLORADO RIVER.

1. General View.

THE Country drained by the Colorado River is a peculiar region. It is a country of plateaus and cañons, the plateaus mainly arid and sterile, where the few streams flow in deep gorges far below the surface.

The longest and most northern branch of the Colorado is Green River, which heads in the Wind River Mountains, against the sources of the Big Horn and the Snake Rivers. This stream, in its long course towards the south, receives the waters of the Uintah from the west, and the Yampa and White Rivers from the east. Near latitude 38° 15', and longitude 110°, it is joined by the Grand River, a stream of nearly equal size, which heads in Middle Park, Colorado, drawing its first supplies of water from the snow-fields of Long's Peak. The stream below the junction of these two forks is known as the Colorado.

Below their junction, the principal branches of the Colorado from the east are the San Juan, the Colorado Chiquito or Flax River, William's Fork, and the Gila; on the west, the "Dirty Devil," Paria, and Virgin.

This region is limited on the east, north, and northwest by high mountain ranges. Its surface is nearly flat, but by no means unbroken. There is little rolling or undulating country. Changes of level take place by very

gentle uniform slopes, or by abrupt precipitous steps. A large part of the surface consists of bare rocks, with no soil or vegetation. A part is covered with a thin sandy soil, which supports a growth of sage and cacti, or even a few piñon pines and cedars. The only vegetation is that eminently characteristic of an arid country.

This aridity has modified orographic forms to an astonishing degree. Where, under different climatic conditions, there would be produced a region similar in most respects to the prairies of the Mississippi Valley, we find a country, flat indeed, or inclined at low angles, but one whose watercourses are far beneath the general level, deep down in cañons, hundreds, thousands of feet beneath the surface.

Great cliffs, thousands of feet in height, and extending like huge walls for hundreds of miles, change the level of the country at a single step.

Isolated buttes and mesas, of great height, are scattered over the plateaus, indicating the former height of the plain of which they formed parts.

"The landscape everywhere, away from the river, is of rock-cliffs of rock, tables of rock, plateaus of rock, terraces of rock, crags of rock,-ten thousand strangely carved forms. Rocks everywhere, and no vegetation; no soil; no land. . . . When speaking of these rocks, we must not conceive of piles of boulders, or heaps of fragments, but a whole land of naked rock, with giant forms carved on it; cathedral-shaped buttes, towering hundreds or thousands of feet; cliffs that cannot be scaled, and cañon walls that shrink the river into insignificance, with vast hollow domes and tall pinnacles, and shafts set on the verge overhead, and all highly coloured-buff, gray, red, brown, and chocolate; never lichened, never mosscovered, but bare and often polished."

The above description by Major J. W. Powell, who

has explored the cañons of the Colorado, gives a graphic pen-picture of the lower and more arid plateaus of this region.

Nearly every watercourse, whether perennial or not, is a cañon; a narrow valley, with precipitous walls, often of enormous height. In many cases these cañons are so numerous that they cut the plateau into shreds—a mere skeleton of a country. Of such a section, Lieutenat Ives, who explored the course of the Lower Colorado, writes:"The extent and magnitude of the system of cañons in that direction is astounding. The plateau is cut into shreds by these gigantic chasms, and resembles a vast ruin. Belts of country, miles in width, have been swept away, leaving only isolated mountains standing in the gap; fissures so profound that the eye cannot penetrate their depths are separated by walls whose thickness one can almost span; and slender spires, that seem tottering on their base, shoot up a thousand feet from vaults below."

But few of these cañons contain water throughout the year. Most of them are dry at all times excepting for a few days in the early spring, or for a few minutes or hours at most after a heavy shower. It is a characteristic of western North America, as of all arid countries, that the streams, away from their sources in the mountains. lose water, rather than gain it, in traversing the lower country. The dry atmosphere and the thirsty soil absorb it, and, in very many cases, large streams entirely disappear in this way. This is the case to a great extent in the plateau country, and still more so in the Great Basin, where these are the only outlets to the drainage.

A few words will suffice to sketch the manner in which the climate has acted in producing these strange and unique orographic effects. The great degree of aridity of the atmosphere, and the slight rainfall, coupled with its