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at the foot of such lofty, rough crested hills, rain, indeed, must be scarce, yet the evidences of running water are displayed in the base of the triangular valleys leading out from the range, where large stones are washed out of the clay and sand and heaped together, the result of existing causes.

The temperature at Carrizo on the 3d June at noon was 100° Fahrenheit, and rose to 102° later in the day. The effect of this heat was visible on the stream, which ceased flowing about 11 o'clock, and did not recommence until near 4 p. m., being absorbed or evaporated during the interval ; two miles below it completely disappears in the sand. Five miles below camp is the high terrace mesa, on gaining which may be seen the desert, as far eastward as the eye can reach. To gain this the river bed was travelled down and its direction followed, for a few miles, where the valley widened into a flat water bottom, the reservoir of the Carrizo ; in front, was the denuded wall of the sands and clays, forming the terrace alluded to, and on the west lay the volcanic rocks, which we were leaving behind, and which stretch out eastward in isolated mountains, forming an unconnected chain, and by contrast to the even surface of the desert resembling, what no doubt they were at one time, headlands and promontories of a bold shore jutting out seaward.

From the edge of the terrace to Sackett's wells is about twelve miles. The soil along the trail is made up of rounded quartz pebbles, grains of felspar, and larger pieces of the minerals mixed ; a yellowish brown fine sand, with some plates of mica, and occasionally small masses of purplish felspar porphyry, all rounded and well polished. Mr. Wm. P. Blake, in Lieut. Williamson's Report, 1853, (H. Doc. 129,) no doubt gives the true explanation of the polishing of these pebbles by the attrition of the loose sands, drifted by the winds.

The unconnected chain of igneous rocks, referred to above, run out about forty-five miles into the desert. One of these lies north of the trail, and one to the south, separating it from the Gulf of California. One of the most remarkable of these is "Signal mountain," which serves as a landmark to travellers from Fort Yuma to San Diego. These hills, judging from their outline, are granitic and porphyritic, with trachyte. Although at a distance they appear like a connected range, yet, when examined carefully, it may be seen that many of them drop down at their extremities, and can be travelled round. Indeed, there cannot be truly said to be any distinct range running eastward from the Sierra Nevada, the general character of the country being a series of extended plains, separated from each other by isolated ridges or lone hills, whose general direction is north 40° west, and south 40° east.

The water supply at Sackett's wells consists of three wells sunk in an arroyo bed, which itself lies four feet below the general level; the wells are about six feet deep, and the water oozes in about five feet down, flowing through a thin stratum of sand which overlies the clay bed constituting the bottom of the wells. Should this last be cut through, the water sinks, and it would be necessary to go several feet down to meet another clay layer. A fourth well was dug at this time by a Mexican party travelling along. The water is good, not saline, and agreeable to the taste ; it oozes out of the sand layer slowly but steadily, requiring six minutes to fill a two-gallon pail. In one of the wells a barrel has been sunk, which should be done with all, and an adobe building should be raised around them. The clay at the bottom of the wells is a yellow, tenacious argil, and advantage might be made of it for brick manufacture, or using it merely puddled as a material for the sides of the wells.

From Sackett's wells to Alamo Mocho is thirty-five miles, passing by Lagoons, the trail lying along a heavy sand road. The sand is fine, white, rounded quartz, like beach sand ; the clay

LAGOONS—ALAMO MOCHO. 123

gradually disappearing the greater the distance from Sackett's wells. In the proximity of the Lagoons the trail was on hard clay, and thence to Alamo Mocho it was mostly sand. This may he looked upon as the most sterile part of the whole desert, on many thousand acres there not being a blade of any vegetable growth. In several places a thin pellicle of clay, two to three inches deep, covers the surface, over which are scattered thin and worn specimens of Anodonta, and some small univalve Gasteropods.

The southeast wind, rising in the afternoon, and blowing with considerable force, carries quantities of the fine sand with it, rendering it intolerably hot and scorching to the eyes; raising the temperature often to 115° Fah.

The " Lagoons," which are occasionally filled by overflows of the Colorado river, (distant 52 miles,) were, at the period of visit, perfectly dry at Alamo Mocho, so called from the stunted and deformed cotton-wood tree near the springs ;* the water is in the bed of the New river, so called, as being the new course which the Colorado took in its overflow of 1849. The channel bends at this point, and is considerably below the level of its bank upon one side, where yellowish red stratified sand, 35 feet high, abut upon its edge. A new well has been sunk lately by the United States goverment, which is 22 feet deep, and yields an ample supply of water, not less than 500 gallons being removed in 2\ or 3 hours ; which, though it had an evident effect in lowering the well, yet its place was quickly supplied by a fresh influx of water. The well is defended by a wooden shaft and plank work to keep the sand from caving in, which is carried up 4$ feet above the level of the surface ; a bucket and windlass would be a great boon to this spot, although found difficult to keep them. Two older wells are at a few yards distance along the same line. In one, the timbers have yielded and decayed, and the well is useless ; the other is in good order, but does not yield so large a supply as the new well.

The whole level plain of the desert at Alamos slopes gently to the south, and in this direction also runs New river bed to meet the Colorado. The line of the bed can be traced by the cottonwoods and mesquite, which are only found growing there. On the level of the desert there is nothing but obione and larrea, the absence of vegetation being thus shown to be due, not to any infertility of the ingredients of the soil, but to the absence of sufficient moisture at the time when vegetable growth requires it.

There is much more moisture in the air at this part of the desert than further west, at Carrizo. Hills 8 and 10 miles off were indistinct and hazy in outline, neither were the stars so distinctly visible; but no dew falls at night, the earth not cooling down sufficient to deposit the moisture from the atmosphere, consequently vegetation suffers almost as much as if the air were wholly deprived of it. Low clouds form in the north/near the horizon, and interchange sheet lightning in distant flashes.f

The gravel pebbles of the desert are made up of volcanic and silicious material, chiefly the former, of which the reddish porphyry is most abundant; hyalitic quartz pebbles are common, with hornstone, chalcedony, phrenite, and chabasite, all rounded and polished by attrition so as to be perfectly smooth to the touch ; small fragments are also scattered about there.

The trail from Alamo Mocho to Cook's well is along the bank of the New river. The surface of the trail between these two waters (22 miles) is more undulating than the former portions of the road, and is alternately a sandy and clayey floor. The sand along this route appears to have drifted in heaps over raised clay mounds ; these, at first sight, appear to he sand banks, 3 to 5 feet high, which have drifted and collected round the stems of mesquite ; but observation shows that those shrubs have grown there when the bank was at that upper level, or nearly so, and while these banks are sand above they are mainly clay below ; their formation is more due to water than to wind. At Cook's well the terrace bank is 30 feet above the well, which is here in a bed similar to that at Alamo ; there is but one well or spring, 4 feet across, and having water in it about 3 feet deep ; its taste is clayey and slightly hard ; the well does not refill readily and requires to be deepened. As the soil is more moist here than at Alamo, a shaft sunk to a depth of 20 feet ought to afford a bountiful supply of water.

°" Mocho," Sp. lopped, maimed—by many this word has been mistaken as being " mucho "—plentiful—but cotton, woods are not abundant here ; it is too dry a situation for them, while the disfigured tree is not many yards distant from the well.

t These phenomena occurred during the prevalence of the soutli wind, which, blowing from the Gulf, may have proluced a condition of atmosphere not often found in this region.

The mesquite between these two waters was flourishing, and, about Cook's well, in pod and very abundant. Yet there were passed groves of cotton-wood trees which were standing, but dead ; some few had fallen, but were, owing to the dryness of the air, but little decayed. The scene presented the curious anomaly of one class of trees flourishing in the immediate vicinity of the dead trunks of another species. To what change of local conditions could this be due? Some have believed in the elevation of the soil, by which it became too dry to sustain these water-loving trees. But while the proofs of elevation are general,* there is no local evidence to support this view ; besides, at higher levels at present, that is, at Alamo Mocho, a few flourishing cotton-wood trees exist. The cause, like the effect, is no doubt local, and may be attributed to the lessened supply of water from the Colorado river reaching this point.

The belief that the waters of the Colorado have only recently flowed into and formed New river is evidently an erroneous one ; a single fluviatile eruption could not have formed the deep and well worn trough which is displayed at the Alamo. At the present time, the lower stratified sands of the desert are water-soaked by the Colorado river; the wells at Indian wells, (not visited,) at Alamo, and Cook's well, are the waters of the Colorado filtered through, and at no remote period that river may have, at the time of freshets, annually rolled its waters through New river bed. The Colorado, from the point where it leaves Fort Yuma until it debouches into the Gulf, resembles, to some extent, the Mississippi; it changes its banks by washing them away, and it forms levees for itself, so as to become higher than the vicinity ; an increased freshet, or an obstruction to the flow of the water by a south wind in the Gulf, may so raise the river level as to overflow or remove its banks and flood the adjacent lands. Cook's wells may have been from some such cause, until very lately, supplied with a much larger amount of moisture, which enabled the cotton-wood trees to grow on the desert level, and the sudden withdrawal of which may have been the cause of their death.

By such occasional overflows of the river upon this district may have been formed the rounded patches of clay, covered with sand, resembling "domes" in miniature, to which reference has been made.

From Cook's well to the Colorado the trail slowly descends off the terrace bank to the river edge. At Algodones is an Indian built village beside some low sand hills, which here lie at the margin of the river ; along this trail an elevated terrace continues on the left hand (or northeast) the whole distance to Fort Yuma; it is more than 30 feet high, is covered up by drifted sands which round its outliue, but it presents very much the appearance of an ancient river line or bank.

At Algodones, a slight elevation of porphyry pebbles, cemented by argillaceous and COLORADO DESERT—UNUSUAL TEMPERATURE. 125

calcareous paste, occurs ; it forms in places a compact rock, and, lying upon the tertiary clays of the desert, may belong to the modern period.

From Algodones to Fort Yuma the trail is along the river bank, (right,) which yields a dense growth of willow and cotton-wood. Continual inroads were being made by the river sweeping away the right bank, destroying the old trail; as much as six feet of the bank has been removed during one night, (June 8.) The river waters were very turbid with (red) mud, high, though declining, and flowed at a rate of five to six miles an hour, ten feet below the level of the bank, two miles below the fort.

It is to be regretted that the rapid transit over the desert, and the period of the year (June) in which it occurred, rendered it, from the insupportable heat, impossible to make a more detailed examination than that contained in these pages. Owing to the excessive heat the marches were made in the evening and night time, and the day was passed in tent to seek repose and avoid the temperature, which, commencing at sunrise with 85° or 90° Fah., would reach 100° at noon, and 117° at 3 o'clock p. m. A hasty and necessarily imperfect survey was all which could be made under such circumstances. The increased temperature of the desert may be due to two causes: one, the level and low surface of the region, causing reverberation of the rays of heat from the lofty hills on the west side, and from the occasional covering of fine, bright sand on its surface ; the other, the chief one, is tbe presence of the sand in the air, which, as so much solid matter in a heated fluid, conveys the warmth more readily to those surfaces which it touches. The southeast wind, which springs up in the afternoon, always carries with it large quantities of sand, blinding the eyes and scorching the skin. The highest ascertained temperature of air alone, examined under circumstances free from the effects of radiation or convection, has been that of 110°.6 Fah., determined by Ruppel at Ambokul, Abyssinia; while on the great African desert the fine grains of sand floating in the air form centres of radiant heat, elevating the temperature to 122°, and even 133° Fah., in the shade, in the oasis of Mourzouk. The horizontal tabular masses of granite and syenite which form flat expanses of naked rock—expanses some thousand feet in diameter, may serve to aggravate the temperature.

Of the injurious effect of the excessive heat and long marches, without water, upon cattle and sheep, there are abundant evidences in the Colorado desert. Skulls, limbs, and whole skeletons of animals lie strewed about along the trail near the watering places. Most of these were on the way to California from Santa Fe and the plains of New Mexico and Sonora, and, overcome by the fatigue and drought, succumbed to nature. Their bleached bones and preserved skins have rendered their last remains unpalatable to the coyote and wolf, and are a valuable, though melancholy, testimony of the dryness of the air.

The Colorado desert, where crossed by this trail, must be looked upon as a deep trough, scooped out at the western side of the continent; its boundary on the west is the only well defined one. There the Cordilleras rise abruptly like a wall; to the north the line of demarcation may be drawn by the termination southwards of these isolated ranges and lone hills, which dot over the surface northeast of Carrizo ; these extend northward into a hill country not yet explored, but which can differ but little from the districts south and north of it; more north of this hill country is the Mojave valley, a region of small ranges and isolated valleys, whose general character, during the greater portion of the year, is sterility ; and such is the whole character of the country to Salt Lake valley, the only difference in climate and vegetation being due to the gradual ascent from 100 feet above sea level to nearly 4,000 feet.

On the east the desert is considered to terminate at the Colorado, but for 100 miles east of that river the general sterile aspect still remains, except in situations where water abounds or irrigation is practised ; this slope is a very gradual one. Southwards the desert continues into Sonora, and embraces the apex of the Gulf of California. The whole area embraced within these limits bears unmistakable evidence of having been an extensive sea bottom at a comparatively recent geological epoch—an extensive gulf, whose only representative now is that of California. The only present evidences of volcanic force are the frequent earthquakes, and the existence of the mud volcanoes south of New river.

Into this sea rolled the Gila, the Colorado, Santa Maria, and Virgin rivers, and it is to the wash of these rivers, delivering their fine matters to be drifted and deposited, that the extensive and numerous beds of clay (alluvium) may be attributed ; while from the western shores of the bay, the Cordilleras, were derived the immensely thick deposits of rolled and stratified loose material, gravels and sand, which underlie the alluvium. At this time were formed the fawncolored unconsolidated sandstone of the Mojave slope of the Cordilleras. The granitic conglomerates at Carrizo belong to this period also, as may also be included the loose conglomerates of the Mojave, near Soda lake. The Cordilleras rose by successive elevations. The first upheave being the protrusion of the mass of granite which carried before it the gneiss and metamorphic rock lying above it; these it broke up, contorted, and, in part, even included in its not yet fully solidified mass. Then followed the period of rest, in which were deposited the Miocene tertiaries of the west flanks of the sierra, no corresponding beds of which are found to the east. This period of rest was followed by the upheaval of the felspar, porphyry, protogine, and trachytic rocks. Then a second calm, in which a conglomerate, including these volcanic rocks with syenite, occurred. Then a third uplift, raising these conglomerates at an angle. The trappean rocks at San Pasquale and on the west of sierra may be connected with this uplift. Previous to the last uplift were deposited the sands and gravels of the desert, with the loose conglomerates, and, posterior to it, when as yet the sea water had not wholly retired, the clay silt beds of the surface subsided. At this period, likewise, may have been formed the terrace extending from Fort Yuma to Pilot Knob. The elevation of the red felspar, porphyry, and trachytic rocks of the Mojave valley are, judging from their lithological character, coeval with the most western uplifts of the Coast Ranges of California, and, therefore, much later than the mass of the Cordilleras, which may be looked upon as occurring at the close of the Miocene period. That any portion of this country was under water recently, or within traditional record, is unlikely. The old Spanish belief that Alta (?) California was an island, is but an instance of erroneous information, rather than a proof; and the tradition of the Cohuilla Indians, who relate the expulsion of their ancestors from off the plains by the rising of the waters, can scarcely be credited, since such irruption should destroy all traces of the water, now cut so deeply in the sands and gravels ; recent falls of rain in a dry country cannot account for excavations made so deeply within so short a period as a few centuries, for tradition can go no higher. Some shadow of support has been afforded these conjectures by the barometrical readings on Lieutenant Williamson's survey, which shows that Cohuilla springs and Salt creek are, respectively, 90 and 42 feet below sea level; but the correctness of the inference derived from these readings may be doubted. The comparison of thermometers, one of which was at Benicia, and the other some hundred miles distant, is liable to grave errors. The altitude of Fort Yuma is found to be nearly 130 feet above former calculations, and a like error may vitiate the readings on the desert. While, then, assuming the general level of the desert to be unusually depressed, we are scarcely warranted in saying that extensive levels are lower than the surface of the sea.

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