Across Southern Arizona.
As you rise up from the Colorado Desert, crossing the river to the east, you meet with a great plain or so-called mesa that extends far across Southern Arizona and Sonora almost up to the Continental Divide. It is broken by short ranges of barren mountains, that have the general trend of the main Sierra Madre, and it looks so much like the country to the west of the river that it is usually recognized as a part of the desert, or at the least “desert country.”
Rising up from the desert.
The great mesas.
It is, however, somewhat different from the Bottom of the Bowl or even the valleys of the Mojave. The elevation, for one thing, gives it another character. The rise from bench to bench is very gradual, and to the ordinary observer hardly perceptible; but nevertheless when the foot-hills of the Santa Rita Mountains are reached, the altitude is four thousand feet or more. There is a difference in light, sky, color, air; even some change in the surface of the earth. The fine sands of the lower desert and the sea-bed silts are missing; the mesas lie close up to the mountains and receive the first coarse wash from the sides; the barrancas on the mountain-sides are choked with great masses of fallen rock, with bowlders of granite, with blocks of blackened lava. The arroyos that carry the wash from the mountains—mere ditches and trenches cut through the mesas—are filled with rounded stones, coarse sands, glittering scales of mica, bits of quartz, breaks of agate and carnelian. The mesas themselves are made up of sand and gravel, sometimes long shelvings of horizontal rocks, sometimes patches of terra-cotta, rifts of copper shale, or beds of parti-colored clay.
“Grease wood” plains.
Upland vegetation.
There is more rain in this upland country and consequently more vegetation than down below. Grease wood grows everywhere and is the principal green thing in sight. So predominant is it that the term “grease wood plains” is not inappropriate to the whole region. Groves of sahuaro stand in the valleys and reach up and over the mountain-tops, chollas and nopals are on the flats; the mesquite grows in miniature forests. But besides these there are bushes and trees not seen in the basin. Palo fierro, palo blanco, cottonwood live along the dry river-beds, white and black sage on the mesas, white and black oaks in the foot-hills. Then, too, there are patches of pale yellow sun-dried grass covering many acres, great beds of evening primrose, and fields covered with the purple salt-bush. It is quite another country when you come to examine it piece by piece.
Grass plains.
As you rise higher and higher to the Continental Divide the whole face of the mesa undergoes a further change. It slips imperceptibly into a grass plain, stretching flat as far as the eye can see, covered with whitened grass, and marked by clumps of yuccas slowly growing into yucca palms. No rocks, trees, cacti, or grease wood; no primrose, wild gourd, or verbena. Nothing but yucca palms, bleached grass, blue sky, and lilac mountains. It is still in kind a desert country, and it is still called a mesa or table-land; but its character is changed into something like the great flat lands of Nebraska or the broken plateau country of Montana.