The morning of the 22d was clear and bright, and a snowy peak to the southward shone out high and sharply defined. As has been usual since we crossed the mountains and descended into the hot plains, we had a gale of wind. We traveled down the right bank of the stream, over sands which are somewhat loose, and have no verdure, but are occupied by various shrubs. A clear bold stream, 60 feet wide, and several feet deep, had a strange appearance, running between perfectly naked banks of sand. The eye, however, is somewhat relieved by willows, and the beautiful green of the sweet cottonwoods with which it is well wooded. As we followed along its course, the river, instead of growing constantly larger, gradually dwindled away, as it was absorbed by the sand. We were now careful to take the old camping-places of the annual Santa Fé caravans, which, luckily for us, had not yet made their yearly passage. A drove of several thousand horses and mules would entirely have swept away the scanty grass at the watering places, and we should have been obliged to leave the road to obtain subsistence for our animals. After riding 20 miles in a north- easterly direction, we found an old encampment, where we halted.

By observation, the elevation of this encampment is 2,250 feet.

23d.--The trail followed still along the river, which, in the course of the morning, entirely disappeared. We continued along the dry bed, in which, after an interval of about 16 miles, the water reappeared in some low places, well timbered with cottonwood and willow, where was another of the customary camping-grounds. Here a party of six Indians came into camp, poor and hungry, and quite in keeping with the character of the country. Their arms were bows of unusual length, and each had a large gourd, strengthened with meshes of cord, in which he carried water. They proved to be the Mohahve Indians mentioned by our recent guide; and from one of them, who spoke Spanish fluently, I obtained some interesting information, which I would be glad to introduce here. An account of the people inhabiting this region would undoubtedly possess interest for the civilized world. Our journey homewards was fruitful in incident; and the country through which we traveled, although a desert, afforded much to excite the curiosity of the botanist; but limited time, and the rapidly advancing season for active operations, oblige me to omit all extended descriptions, and hurry briefly to the conclusion of this report.

The Indian who spoke Spanish had been educated for a number of years at one of the Spanish missions, and, at the breaking up of those establishments, had returned to the mountains, where he had been found by a party of Mohahve (sometimes called Amuchaba) Indians, among whom he had ever since resided.

He spoke of the leader of the present party as "mi amo," (my master.) He said they lived upon a large river in the southeast, which the "soldiers called the Rio Colorado;" but that, formerly, a portion of them lived upon this river, and among the mountains which had bounded the river valley to the northward during the day, and that here along the river they had raised various kinds of melons. They sometimes came over to trade with the Indians of the Sierra, bringing with them blankets and goods manufactured by the Monquis and other Colorado Indians. They rarely carried home horses, on account of the difficulty of getting them across the desert, and of guarding them afterwards from the Pa-utah Indians, who inhabit the Sierra, at the head of the Rio Virgen, (river of the Virgin.)

He informed us that, a short distance below, this river finally disappeared. The two different portions in which water is found had received from the priests two different names; and subsequently I heard it called by the Spaniards the Rio de las Animas, but on the map we have called it the Mohahve river.

24th.--We continued down the stream (or rather its bed) for about eight miles, where there was water still in several holes, and encamped. The caravans sometimes continued below, to the end of the river, from which there is a very long jornada of perhaps 60 miles, without water. Here a singular and new species of acacia, with spiral pods or seed- vessels, made its first appearance; becoming henceforward, for a considerable distance, the characteristic tree. It was here comparatively large, being about 20 feet in height, with a full and spreading top, the lower branches declining towards the ground. It afterwards occurred of smaller size, frequently in groves, and is very fragrant. It has been called by Dr. Torrey, spirolobium odoratum. The zygophyllaceous shrub had been constantly characteristic of the plains along the river; and here, among many new plants, a new and very remarkable species of eriogonum (eriogonum inflatum, Tor. & Frem.) made its first appearance.

Our cattle had become so tired and poor by this fatiguing traveling, that three of them were killed here, and the meat dried. The Indians had now an occasion for a great feast and were occupied the remainder of the day and all night in cooking and eating. There was no part of the animal for which they did not find some use, except the bones. In the afternoon we were surprised by the sudden appearance in the camp of two Mexicans--a man and a boy. The name of the man was Andreas Fuentes; and that of the boy, (a handsome lad, 11 years old,) Pablo Hernandez. They belonged to a party consisting of six persons, the remaining four being the wife of Fuentes, and the father and mother of Pablo, and Santiago Giacome, a resident of New Mexico. With a cavalcade of about thirty horses, they had come out from Puebla de los Angeles, near the coast, under the guidance of Giacome, in advance of the great caravan, in order to travel more at leisure, and obtain better grass. Having advanced as far into the desert as was considered consistent with their safety, they halted at the Archilette, one of the customary camping-grounds, about 80 miles from our encampment, where there is a spring of good water, with sufficient grass; and concluded to await there the arrival of the great caravan. Several Indians were soon discovered lurking about the camp, who, in a day or two after, came in, and, after behaving in a very friendly manner, took their leave, without awakening any suspicions. Their deportment begat a security which proved fatal. In a few days afterwards, suddenly a party of about one hundred Indians appeared in sight, advancing towards the camp. It was too late, or they seemed not to have presence of mind to take proper measures of safety; and the Indians charged down into their camp, shouting as they advanced, and discharging flights of arrows. Pablo and Fuentes were on horse-guard at the time, and mounted according to the custom of the country. One of the principal objects of the Indians was to get possession of the horses, and part of them immediately surrounded the band; but, in obedience to the shouts of Giacome, Fuentes drove the animals over and through the assailants, in spite of their arrows; and, abandoning the rest to their fate, carried them off at speed across the plain. Knowing that they would be pursued by the Indians, without making any halt except to shift their saddles to other horses, they drove them on for about sixty miles, and this morning left them at a watering-place on the trail, called Agua de Tomaso. Without giving themselves any time for rest, they hurried on, hoping to meet the Spanish caravan, when they discovered my camp. I received them kindly, taking them into my own mess, and promised them such aid as circumstances might put it in my power to give.

25th.--We left the river abruptly, and, turning to the north, regained in a few miles the main trail, (which had left the river sooner than ourselves,) and continued our way across a lower ridge of the mountain, through a miserable tract of sand and gravel. We crossed at intervals the broad beds of dry gullies, where in the seasons of rains and melting snows there would be brooks or rivulets: and at one of these, where there was no indication of water, were several freshly-dug holes, in which there was water at the depth of two feet. These holes had been dug by the wolves, whose keen sense of smell had scented the water under the dry sand. They were nice little wells, narrow, and dug straight down; and we got pleasant water out of them.

The country had now assumed the character of an elevated and mountainous desert; its general features being black, rocky ridges, bald, and destitute of timber, with sandy basins between. Where the sides of these ridges are washed by gullies, the plains below are strewed with beds of large pebbles or rolled stones, destructive to our soft-footed animals, accustomed to the soft plains of the Sacramento valley. Through these sandy basins sometimes struggled a scanty stream, or occurred a hole of water, which furnished camping-grounds for travelers. Frequently in our journey across, snow was visible on the surrounding mountains; but their waters rarely reached the sandy plain below, where we toiled along, oppressed with thirst and a burning sun. But, throughout this nakedness of sand and gravel, were many beautiful plants and flowering shrubs, which occurred in many new species, and with greater variety than we had been accustomed to see in the most luxuriant prairie countries; this was a peculiarity of this desert. Even where no grass would take root, the naked sand would bloom with some rich and rare flower, which found its appropriate home in the arid and barren spot.