Hundreds of people would gather at some of the summer food gathering camps where they not only gathered food, but they also enjoyed such activities as visiting, horse-racing, bone games, trade and exchange, and arranging marriages. Gambling certainly involved transfers of goods from tribe to tribe.
The Cowlitz maintained inter-tribal relationships, and married freely with adjoining tribes, even with the Chinooks who were their longstanding rivals. The Lower and Upper Cowlitz were not on good terms with the tribes on the coast and did not like to go there to trade.
The Cowlitz were a commercial people, and they traded their baskets, blankets, camas, and some slaves. These were transported down the Cowlitz River and up the Columbia to the great Indian mart at Wishram above The Dalles. They were traded for copper beads, obsidian, bear grass for basket weaving and beaded adornment. Indians from the Willamette paddled up the Cowlitz River to trade salmon and trout for camas root.
James G. Swan, speaking in regards to the inter-tribal relationships between the western Washington tribes said, “All the value they set upon their grounds is for hunting and fishing, and the only bounds are such as they set between themselves and neighboring tribes.”
The Cowlitz participated in potlatch ceremonies, which were great giveaways. There are numerous kinds of potlatches, i.e.: Name-giving potlatches (It is considered a very sacred thing to give a name to someone), marriage ceremony potlatches, memorial potlatches wherein a family honors the sacred memory of a deceased family member, etc. After the decimation of the population in the villages, as a result of the intermittent fever, it became necessary in some cases for differing clans, villages or bands to regroup as one village; consequently, some potlatches resulted from the need to choose between two existing chiefs or headmen to determine which one was the most powerful or wisest. The Cowlitz invited other tribes to their name-giving potlatches.