The high mountains now began to draw close to the expedition, and they camped one night at a place called the Gates of the Rocky Mountains. Here tremendous rocks rose directly from the river's edge almost twelve hundred feet in the air; at the base they were made of black granite, but the upper part Lewis decided was probably flint of a yellowish brown and cream color. On July 25th the advance guard reached the three forks of the Missouri. Chaboneau was ill, and they had to wait until Lewis and the others caught up. They named the forks of the river Gallatin, Madison, and Jefferson, in honor of the statesmen of those names. It was at this place that the Indian squaw Sacajawea had been in camp with her tribe five years before when the Minnetarees attacked them, killed some, and made a prisoner of her and some others. Lewis hoped that she would be able to help them if they should fall in with bands of her own tribe. As the main stream ended here, the party now followed the Jefferson River. They soon decided that it would be necessary to secure horses if they were to cross the mountains, and Lewis with three men set out to try to find the Shoshone Indians, from whom they might buy mounts. After several hours' march they saw a man on horseback coming across the plain toward them; examining him through the glass Lewis decided that he belonged to a different tribe of Indians from any that they had yet met, probably the Shoshones. He was armed with a bow and a quiver of arrows, and rode a good horse without a saddle, a small string attached to the lower jaw answering as a bridle. Lewis was anxious to convince him that the white men meant to be friendly, and went toward him at his usual pace. When they were still some distance apart the Indian suddenly stopped. Lewis immediately stopped also, and taking his blanket from his knapsack, and holding it with both hands at the four corners threw it above his head and then unfolded it as he brought it to the ground, as if in the act of spreading it. This signal, which was intended to represent the spreading of a robe as a seat for guests, was the common sign of friendship among the Indian tribes of the Missouri and the Rocky Mountains. Lewis repeated the sign three times, and then taking some beads, a looking-glass, and a few other trinkets from his knapsack, and leaving his gun, walked on toward the Indian. But when he was within two hundred yards of him the Indian turned his horse and began to ride away. Captain Lewis then called to him, using words of the Shoshones. The captain's companions now walked forward, also, and their advance evidently frightened the Indian, for he suddenly whipped his horse and disappeared in a clump of willow bushes. When they returned to the camp Lewis packed some more Indian gifts in his knapsack, and fastened a small United States flag to a pole to be carried by one of the men, which was intended as a friendly signal should the Indians see them advancing.