Much of the material from the Yakima region resembles that which I have seen from the general area including the Columbia Valley between Umatilla and The Dalles, and possibly extending further down the valley. There seems to be a greater similarity of the art products of the Yakima to those of the Thompson River region than to those of the Columbia Valley below the mouth of the Snake, so far as we understand the latter region at this time, and this according to Lewis[433] is certainly not contrary to the belief in an earlier occupancy of this region by the Salish. The culture here resembles that of the Nez Perce region to the east in that a considerable variety of material was used for chipped implements.[434] [433] Lewis, p. 196. [434] Spinden, p. 181. Inter-tribal trade may have been a factor in the production of some observed similarities. It was seen that pipes of three types, one of which is found as far east as the Dakota, another as far north as the Thompson River country, and a third as far west as the Queen Charlotte Islands are all found in this region. It is clear that the ancient people from the Yakima region had extensive communications not only with the region southward as far as The Dalles, but also northward, as far as the more distant Thompson River tribes. If the products of the sea found in this region came up the Columbia, as may be inferred from Lewis,[435] it is a good illustration of how trade as a rule, follows the line of least physical resistance; although the migrations of the tribes do not always follow such lines because the lines of trade as a rule are thickly populated by people who resist the migration of their neighbors. Lewis[436] states that from the coast inward there was only one trade route of importance in the Washington-Oregon-Idaho region and this led up the Columbia River to The Dalles where was found the greatest trade center in the whole region and whither the tribes were wont to come from the north and south as well as from the east.[437] Klamath,[438] Cayuse, Nez Perce, Walla Walla and other Sahaptin and probably Salish tribes were all in the habit of going there to traffic. He also states that further east, the Sahaptin in their turn, traded with the Shoshone from whom they obtained buffalo robes and meat. The center for this trade at least in later times was the Grande Ronde in eastern Oregon;[439] but this later center probably came into being after the advent of the horse. The Okanogan are known to have crossed the mountains to Puget Sound to trade wild hemp for sea shells especially dentalia as well as for other small objects.[440] The Yakima also in later times crossed the mountains and traded with Puget Sound tribes according to Gibbs,[441] but if this trade were carried on in earlier times its effect in the Yakima Valley seems to have been slight as indicated by the few dentalium shells, the shell pendants shown in Figs. 87-94 and the pipe of coast art, shown in Fig. 127.