A few miles above our mid-day encampment, we entered the valley of a small creek, tributary from the south-east to the stream we had been ascending; but this we found so narrow and so obstructed by fallen masses of rock, and almost impenetrable thickets of alders and willows, as to render our progress extremely tedious and painful. We were several times induced to attempt passing along the bed of the stream, but as the mud was in many places very deep, this was done at the cost of the most violent and fatiguing exertions on the part of our horses, and the risk to ourselves of being thrown with our baggage into the stream. With the hope of finding an easier route across the hills, we ascended with much difficulty a craggy and abrupt ravine, until we had attained nearly the elevation of the precipitous ramparts which hemmed in the narrow valley of the creek; but all we gained by this ascent was the opportunity of looking down upon a few of our companions still lingering below, diminished to the stature of dwarfs by the distance, and by contrast with the rude and colossal features of the scene. The surface of the country extending on both sides from the summit of the precipices, consisted of abrupt conic piles, narrow ridges, and shapeless fragments of naked rocks, more impassable than the valley below. Counselled therefore by necessity, we resumed our former course, ascending along the bed of the creek.[45] Among other birds which occurred in this day's march, we noticed the yellow-bellied fly catcher and the obscure wren. One of the small striped ground-squirrels already noticed was killed, and an individual belonging to another species,[46] distinguished by the extraordinary coarseness and flattened form of the fur, and by three black lines on each side of the tail; these {260} lines at their tips are of course united over the surface of the tail as in the Barbary squirrel. It nestles in holds and crevices of the rocks, and does not appear to ascend trees voluntarily. It appears to inhabit principally about the naked parts of the sandstone cliffs, or where there are only a few cedar bushes. In the pouch of the specimens killed, we found the buds and leaves of a few small plants, common among the rocks. Following up the bed of the creek, we ascended by a gradual elevation to the surface of the stratum of red sandstone. It is separated by a somewhat distinct boundary from the finer and more compact grey variety which rests upon it. This grey sandstone appears from the organic relics it contains, as well as from its relative position, to have been of more recent deposition than the red. Its prevailing colours are grey or yellowish white; its stratifications distinct; and its cement often argillaceous.