The site of Seaside was first inhabited by the Clatsop Indians whose ancestors had lived for thousands of years before the coming of the white man in the far northwest corner of present- day Oregon. Clatsop territory encompassed some 1100 square miles; its northern border, the Columbia River, extended upstream to the Tongue Point area, there forming an eastern border through the Coast Range wilderness to a border at the south running west to Tillamook Head; its western border, the Pacific Ocean, reached north to the mouth of the Columbia. This homeland offered dense forests of fir, pine, spruce and cedar, as well as fertile coastal plains, creating an abundance of game, berries and edible roots. Its waters--the Columbia, streams and lakes, ocean tidelands--teemed with life including many species of salmon, freshwater fish, and shellfish.

The Necanicum River, draining the south Clatsop region, nurtured groves of fir, spruce and pine, a rich groundcover including salal, kinnikinnik, wapato and camass, interspersed with meadows and berry thickets. Here, where the Necanicum empties into the Pacific, massive boulders and rocks identify the terminal moraine of ancient Necanicum Glacier that formed the canyon of the river and merged with the Pacific in this area.

Fourteen Clatsop villages are known to have existed. One, Quatat, stood at the mouth of the Necanicum; two others, Ne-ah-coxie and Ne-co-tat, were nearby. Indian artifacts and skeletal remains continue to be unearthed in and around Seaside. Building excavations have brought up draw knives, gouges, implements, wampum, and other trading and personal effects. A portion of Seaside west of the Necanicum was once an ancient Indian burial ground. Like their cousins, the Chinooks north of the Columbia, the Clatsops were canoe people who buried the dead in their canoes with personal effects needed in the next life. The canoes were braced atop four upright split timbers that had been sunk a few feet in the ground. Skulls identify these people as Clatsop Flatheads--so called because of their sloping foreheads, a result of their practice of binding the infant across its brow with a strong piece of bark or wood that was tied firmly at both ends to the cradleboard. This provided ease of transport by the mother, as well as a flattening effect of the frontal skull.