We had camped some distance from the trail, and having taken our horses over the ridge into another ravine, had picketed them on the best grass that could be found. It was my duty to stand guard and watch the horses until midnight. The night was clear and still, and although it was bright starlight, it seemed to be very dark in the ravine. I took a position slightly up the hillside and reclined with ear near the ground. About midnight there came seemingly from some very distant source, a low, deep, rumbling roar. For a time it was impossible even to surmise the cause. It seemed to be subterranean and yet it was not an earthquake, for the sound was continuous and gradually increased in depth and power. In a few minutes I became convinced that it was caused by the hoofs of a great number of running horses approaching through the ravine. As a measure of precaution I thought it best to move a little out of the valley to a position behind a growth of sage brush near-by, and there await developments. An Indian raid at midnight was hardly to be suspected, nor had we heard of any large body of cavalry in those parts. The sound increased in power like the roar of an approaching tornado, and an onrushing mass finally swept round the nearest curve in the ravine. Our horses, frightened by the approaching herd, suddenly started in advance, as could be inferred from their snorting and the rattle of the iron picket pins, some of which were pulled from the ground. All were soon in flight. Those which failed at once to escape were carried along the next moment with a solid, resistless tide of oncoming mules which leaped one upon another. As the drove swept by I caught glimpses here and there of the moving forms, which showed that the mules were riderless; being stampeded, their fright was communicated to one another--those in the rear crowding upon those in front; and some of them, I believe, stumbled and were run over by the compact mass that followed. In a moment all had passed; but for a long time in the direction of a range of hills to the west, could be heard the roar of hundreds of hoofs and the ring of the picket pins as they were dragged over the stony ground. The sound did not die away entirely in its slow diminuendo until the mules had passed the range six miles to the west. On visiting the spot where our horses had been picketed, we found that every one of them had been carried away in the mad rush, and unless we could recover them the inconveniences would be most serious. The natural conclusion then was that the large herd had been stampeded by mounted Indians, who would soon follow. When about to return to camp to report the situation to our party, I became conscious of the approach of mounted men from the same direction as that from which the stampede came.