13th.--The night has been cold; the peaks around the lake gleam out brightly in the morning sun, and the thermometer is at zero. We continued up the hollow formed by a small affluent to the lake, and immediately entered an open pine forest on the mountain. The way here was sometimes obstructed by fallen trees, and the snow was four to twelve inches deep. The mules at the gun pulled heavily, and walking was a little laborious. In the midst of the wood, we heard the sound of galloping horses, and were agreeably surprised by the unexpected arrival of our Tlamath chief with several Indians. He seemed to have found his conduct inhospitable in letting the strangers depart without a guide through the snow, and had come, with a few others, to pilot us a day or two on the way. After traveling in an easterly direction through the forest for about four hours, we reached a considerable stream, with a border of good grass; and here, by the advice of our guides, we encamped. It is about thirty feet wide, and two to four feet deep, the water clear, with some current; and, according to the information of our Indians, is the principal affluent to the lake, and the head-water of the Tlamath river.
A very clear sky enabled me to obtain here to-night good observations, including an emersion of the first satellite of Jupiter, which gave for the long. 121° 20' 42", and for the lat. 42° 51' 26". This emersion coincides remarkably well with the result obtained from an occultation at the encampment of December 7th to 8th, 1843; from which place, the line of our survey gives an easting of 13 miles. The day's journey was 12 miles.
14th.--Our road was over a broad mountain, and we rode seven hours in a thick snow-storm, always through pine forests, when we came down upon the head-waters of another stream, on which there was grass. The snow lay deep on the ground, and only the high swamp-grass appeared above. The Indians were thinly clad, and I had remarked during the day that they suffered from cold. This evening they told me that the snow was getting too deep on the mountain, and I could not induce them to go any farther. The stream we had struck issued from the mountain in an easterly direction, turning to the southward a short distance below; and, drawing its course upon the ground, they made us comprehend that it pursued its way for a long distance in that direction, uniting with many other streams, and gradually becoming a great river. Without the subsequent information, which confirmed the opinion, we became immediately satisfied that this water formed the principal stream of the Sacramento river; and, consequently, that this main affluent of the bay of San Francisco had its source within the limits of the United States, and opposite a tributary to the Columbia, and near the head of the Tlamath river, which goes to the ocean north of 42°, and within the United States.