Puget Sound tribes usually had gable roofs with more than one pitch. The Skagits were generally lowlanders, who only ventured into the North Cascades during the summer months, and structures in the mountains were more modest, consisting mostly of temporary buildings erected with poles and covered with branches. The Skagits erected totem poles and participated in potlatch ceremonies, similar to the Haidas, but with less complexity and extravagance. By 1910, only about 56 Skagits remained in the region, but their numbers have since rebounded to several hundred. Inland and residing to the north and east of the Skagit tribe, the Nlaka'pamux (also known as the "Thompson Indians", named after explorer David Thompson), Chelan, Okanogan and Wenatchi (Wenatchee) tribes lived partly or year-round in the eastern sections of the North Cascades. The Skagits and Nlaka'pamux often had disputes, and raided one another's camps in search of slaves or to exact retribution. Like the coastal-based Skagits, inland tribes also constructed long lodges which were occupied by numerous families, though the style of construction was slightly different as the lodges did not have partitions separating one family from another, and were frame constructed and covered with reed mats rather than from cedar planking. One Wenatchee tribal lodge was described by Thompson as being long. Inland tribes were more likely to travel on foot or horseback than by canoe since the inland regions were less densely forested. Inland tribes also had less bountiful fisheries and greater weather extremes due to being further away from the moderating influence of the Pacific Ocean. Inland tribes rarely erected totem poles or participated in potlatch ceremonies. By the beginning of the 20th century, inland tribes, like their coastal neighbors, had experienced population decline from their first contact with white explorers a hundred years earlier, mostly due to smallpox and other diseases. Anglo-European exploration The first white explorer to enter the North Cascades was most likely a Scotsman named Alexander Ross, who was in the employ of the American-owned Pacific Fur Company. To the southeast of the modern park boundary, Ross and other members of the company constructed Fort Okanogan in 1811, as a base from which to operate during the early period of the Pacific Northwest fur trade. Fort Okanogan was the first American settlement in present-day Washington State, well north of the route followed by members of the Lewis and Clark Expedition of 1804–1806, and also north