Ten miles northwest of Heart Lake is Madison Lake, the source of Madison River, the country between being a somewhat rugged range of mountains, of which Red Mountain is the most conspicuous. To the eastward from Heart Lake is Mount Sheridan, from the summit of which a magnificent view of the Yellowstone Basin can be obtained. Nearer the great lake is Flat Mountain, whose altitude falls a little short of 10,000 feet. Between Flat Mountain and the Yellowstone Range the divide is very low, some of the branches of Snake River extending up to within two miles of the lake, where the elevation is not more than 400 feet above the lake level. It is doubtless this singular interlacing of the headwaters of the Yellowstone and Snake River that gave rise to Bridger's story of the "Two Ocean River."
At sunrise on the morning of August 10th, at the west base of Flat Mountain, the thermometer stood at 15½° Fah., and water froze in Dr. Hayden's tent that night a quarter of an inch thick. It was in this neighborhood that Mr. Everts was lost from the first expedition.
The country between Flat Mountain and the hot springs at the southwestern extremity of the lake is a level plateau with alternating spaces of grassy glade and dense thickets of pine around and between a perfect network of small, lily-covered lakes. The hot springs on the lake shore are numerous and of great variety and interest. There are no true geysers, however, though some of the springs are pulsating springs, the water rising and falling in their orifices with great regularity. Higher up the bank are a large number of mud-springs, two or three hundred in all, of variable temperatures, the most of them not differing materially from those already described. Some, however, have a character strikingly unique. The area covered by the springs is about three miles long and half a mile wide, a portion of it reaching out into the lake. Some of the submerged springs have built up funnel-shaped craters of silicious deposit, from five to twenty feet in height, rising from the bottom to the surface of the water. Extending a pole over the deep water, members of Dr. Hayden's party caught trout and cooked them in these boiling springs out in the lake without removing them from the hook.
Four hundred yards from the lake shore is a large boiling basin of pink-colored mud, seventy feet in diameter, with a rim of conical mud craters, which project the hot mud in every direction. The deposit speedily hardens into a firm, laminated stone, of beautiful texture, though the brilliant pink color fades to a chalky white. Near and around this basin are a dozen springs, from six to twenty-five feet across, boiling muddy water of a paint-like consistency, varying in color from pure white to dark yellow. Close by are several flowing springs of clear hot water, from ten to fifty feet in diameter, their basins and channels lined with deposits of red, green, yellow, and black, giving them an appearance of gorgeous splendor. The bright colors are on the surface of the rock only, which is too friable to be preserved. Below these springs are several large craters of bluish water, boiling to the height of two feet in the centre, and discharging large streams of water; their rims are raised a few inches in a delicate rock-margin of a fringe-like appearance, deposited from the water. Beyond these are two lakes of purple water, hot, but not boiling, and giving deposits of great beauty. Near by are two more blue springs, one thirty by forty feet, and 173° in temperature. This spring discharges a considerable stream into the other, which is seventy feet distant, and six feet lower. The latter is forty feet by seventy-five, 183° in temperature, and discharges a stream of one hundred inches. The craters of these springs are lined with a silvery-white deposit of silica, which reflect the light so as to illuminate the water to an immense depth. Both craters have perpendicular but irregular walls, and the distance to which objects are visible down in their deep abysses is truly wonderful.
West of these is another group of clear watered hot springs, which surpass all the rest in singularity if not in beauty. These have basins of different sizes and immeasurable depth, in which float what appear like raw bullock hides as they look in a tanner's vat, waving sluggishly with every undulation of the water. On examination, this leathery substance proves to be of fragile texture, like the vegetable scum of stagnant pools, and brilliantly colored red, yellow, green, etc., black on the under side. This singular substance is about two inches in thickness, jelly-like to the touch, and is composed largely of vegetable matter, which Dr. Hayden thinks to be diatoms.
Of the beautiful transparency of the springs above described, Dr. Hayden says: "So clear was the water that the smallest object could be seen on the sides of the basin; and as the breeze swept across the surface, the ultramarine hue of the transparent depth in the bright sunlight was the most dazzlingly beautiful sight I ever beheld. There were a number of these large clear springs, but not more than two or three that exhibited all those brilliant shades, from deep sea green to ultramarine."
Occasionally, says Lieutenant Doane, this anomaly is seen, namely: "two springs, at different levels, both boiling violently; one pours a large and constant stream into the other, yet the former does not diminish, nor does the latter fill up and overflow."
Most of the springs, however, seem to be independent of each other, since they have different levels at the surface, different temperatures and pulsations, and rarely are the waters and deposits of any two exactly alike.
Passing northward through dense woods and almost impenetrable fire-slashes, the next noteworthy region arrived at is the valley of Bridge Creek, the creek receiving its name from a natural bridge of trachyte thrown across the stream. The bridge is narrow, affording scanty room for the well-worn elk-trail two feet wide, while the descent on either hand is so great that a fall from the bridge would be fatal to man or beast. Numerous herds of elk make daily use of this convenient passway.
Dead and dying springs are abundant all along the valley of this creek, the most of them being reduced to mere steam-vents. In one place the spring deposits cover several acres and present a most attractive picture. The ground is thickly covered with conical mounds, from a few inches in diameter to a hundred feet, full of steaming orifices lined with brillant sulphur-crystals. The under side of the heated crust is everywhere adorned in the same manner. The basis of the deposit is snow-white silica, but it is variegated with every shade of yellow from sulphur, and with scarlet from oxide of iron. From a distance the whole region has the appearance of a vast lime-kiln in full operation. Most of the country has been eroded into rounded hills from fifty to two hundred feet high, composed of the whitish-yellow and pinkish clays and sands of the modern lake deposit, which seems to prevail more or less all round the rim of the basin, reaching several hundred feet above the present level of the lake.