This province displays a great nitmher of the major vegetational 

 hells and zones to he encountered on this continent because at 

 least half of it stands on the true deserts, whereas some of its 

 peaks are high enough to support year-round icefields. It is also 

 unique in that rock strata representing alt known geological 

 ages from the Pre-Cambrian of 750 million years ago to the 

 present are somewhere to be seen on its surface. It is a large, 

 isolated, and well-defined province, being some seven hundred 

 miles from north to south and six hundred miles at its widest. 

 Mount Elbert at the apex of the Colorado area is over 

 14.400 feet high. 



That part of it which is not in the desert is wholly contained 

 within the North Scrub Belt, and this produces some weird 

 effects. Although either wholly mountainous or high plateau, it 

 is edged by pockets of lowlands, it contains one great (the 

 Wyoming) and sundry smaller basins, and its whole center is 

 composed of a sort of fern-frond-shaped gutter drained by 



a single river system — the Colorado. It is formed of five great 

 subprovinces. including three mountainous ones which may be 

 called the Colorado, the Utah, and the Arizona blocks, and 

 two major basins — the Wyoming and the Colorado "Plateau" or 

 better, Platea. The three mountain blocks form a complete ring 

 around the latter, with narrow connecting causeways in the 

 north, west, and east. Oddly, the main river cuts right through 

 the northern of these, but. instead of doing the same through the 

 western on its way out of the platea, it has cut the mighty Grand 

 Canyon through almost the widest and highest stretch of the 

 adjoining mountains and left to one side a natural ouliel 

 dammed by only a narrow neck of highlands. 



Its boundaries are almost everywhere as precise as scacoasts 

 On the east is the edge of the Great Prairie plateau, from 

 which the mountains rise as from an ocean. (Incidentally, the 

 Continental Divide, of which so much has been made, runs down 

 the middle of the east mountain block. Apart from being a 

 watershed, this has no significance and affects neither fauna 

 nor flora.) Its northern edge is equally abrupt and is formed by 

 the southern face of the North Montane Block. Us western edge 

 is a sudden wall-like drop onto the arid Great Basin. Us 

 southern border, from the mouth of the Grand Canyon around 

 the Arizona Block to the upper Rio Grande, is clearly defined 

 topographically but is not so abrupt and is more indented and 

 steplike. In New Mexico its edge turns north and then east 

 across the heads of the Rio Grande and Estancia valleys and over 

 low mountains to the central plains. South and east of this 

 latter line, there is a string of mountain ranges that reaches far 

 to the southeast — the Sacramentos to the Guadalupes. These are 

 clad in the same vegetation as this province's upper mountain 

 slopes and could be classed with it. However, they have closer 

 affinity with the ranges that stretch across the north Mexican 

 desert to the Sierra Oriental, and should be regarded as a 

 transitional subprovince. 



The Wyoming Basin with its many marginal basins is a 

 strange physiographic entity, but from the phytogeographic 

 viewpoint is in no way abnormal, being low in altitude and 

 hence covered with scrub. It is connected on the one hand ivith 

 the central prairies, and on the other, by a narrow channel 

 winding to the nortlnvest. with the Great Basin 



ever, one may readily divide the West into a number of clearly 

 defined natural provinces, each having a unique flora, fauna. 

 climate, and to a great extent geological structure and history. 

 There will nevertheless be two pieces, as it were, left over, and 

 these may be tacked onto this province and described with it. The 

 first is the Wyoming Basin, a scrub-covered, almost circular 

 depression lying north of the province, between it and the North 

 Montane Block. This connects with the great plateau of the 

 central part of the continent on the one side and with the upper 

 region of the Great Basin on the other by means of a narrow, 

 winding gorge. The second appendage is of quite another nature. 



NO-MAN'S LAND 



desert swings away to our left. This scrub continues for some 

 three hundred miles in a slowly widening belt to the southern 

 edge of the South Montane Province, between the Great Prairies 

 and the Chihuahua deserts. The vegetation in this strip is sparse 

 and stunted, and usually clumpy, with thorny shrubs and 

 bunches of desert grass. It has rather an unusual fauna, including 

 pronghorns, enormous numbers of jack rabbits, and some rather 

 specialized lizards. 



As we travel northwestward this vegetation clothes the es- 

 carpment to one's right or north side and becomes progressively 

 arid from the foot of Edwards Plateau to that of the Stockton 

 Escarpment. Here the desert comes up to meet us once more, 

 leaving only the Big Bend Mountains to our left. If we climb 

 this escarpment to the upper Pecos valley on the great plateau 



Going west from the East Chaparrals and following the North 

 Scrub Belt, we proceed up the valley of the Rio Grande via 

 Eagle's Pass which actually lies in the Desert Belt. Somewhat 

 northwest of this point we re-enter the scrublands, while the 



These softly colored dunes are piled against the mighty 

 Sangrc dc Crista Range, in the San Luis Valley in the 

 southern Rockies. They wave and alter farm canstantly. 



198 



