The archaeological site of Cooper’s Ferry site lies along the lower Salmon River near the confluence with Rock Creek in the western part of the state of Idaho in the United States of America. It is located 17 kilometers south of the town of Cottonwood and 63 kilometers upstream from the Snake river [4][1]. 

Cooper’s Ferry was first excavated by Butler in 1961, 1962, and 1964. These excavations revealed a deeply stratified sequence of cultural occupation, including a series of stemmed and lanceolate projectile points [5].  In 1997, Davis led another excavation on the site. These excavations revealed human occupation spanning the late Pleistocene and early Holocene periods [6]. During excavation, the team discovered a Western Stemmed Tradition (WST) cache dated to 13,115 to 13,300 cal BP and 13,060 to 13,475 cal BP [4][7][3]. Davis returned to the site in 2009 up to 2018 to conduct more extensive excavations [7][3].

Finds

The site includes two dig areas: Areas A and B. Area A produced several hundred artefacts, including stone tools dating from 13,200 to 16,000, charcoal, fire-cracked rock, and bone fragments from medium- to large-bodied animals. Also found were evidence of a fire hearth, a food processing station, and other pits created as part of domestic activities at the site. The team also uncovered tooth fragments from an extinct horse known to have lived in North America at the end of the last glacial period [3][8].

An artefact cache found at the site containing Western Stemmed Tradition (WST) projectile points in a clearly defined pit feature offers a unique perspective on early lithic technology and logistical organization in western North America. Some of the points were made from cryptocrystalline silicates found 16km away from Cooper’s Ferry. These tools appear to belong to a generalized toolkit that was probably there for future use [4]. 

During the 2012 to 2013 excavations, fourteen additional stemmed projectile points of similar design were discovered, thirteen of which were found in situ. Thirteen were made of cryptocrystalline silicate while one was of fine-grained igneous material, possibly basalt [7]. A number of the site’s WST projectile points were created by pressure flaking a linear macroblade or macroflake blank that was only slightly larger than the final product [4][7]. 

Separate excavations conducted in Area B uncovered additional contemporaneous evidence of the site’s early cultural occupation. Consistent radiocarbon dates from the lowest cultural deposits in Area B range from 13,260±240 to 13,091±48 BP (16,675 to15,240 cal BP to 15,772 to 15,617 cal BP), helping confirm the early age estimates from Area A. Fourteen complete and fragmentary stemmed projectile points, other stone tools, substantial amounts of lithic debris, and animal bone fragments were recovered. These projectile points are 2,300 years older than those found in Area A. Twelve were made of cryptocrystalline silicate and two were made of fine-grained volcanic rock. Most of these projectile points are relatively small and made on elongate flakes with minimal bifacial reduction. Four larger points were more extensively reduced from bifacial preforms [9].

The shape of the stemmed points and the lithic technology used to produce them are similar to bifacial points found in northeast Asia, particularly northern Japan, dating to the Late Upper Paleolithic (21,400 to 16,170 BP). Combined dates from Areas A and B suggest that the initial occupation of Cooper’s Ferry was at 15,725 to 16,045 cal BP with intermittent occupation that continued until 11,800 to 13,450 cal BP [9]. 

The 16,000 dates from the oldest artefacts from Cooper’s Ferry challenged the “Clovis First”  theory of early migration in America. Clovis stone tools were considered the first human technology in America. It was believed that early humans crossed from Siberia to America through an opening in the ice sheet near the present-day Dakotas, and this ice-free corridor was hypothesized to have opened up 14,800 years ago. The earlier dates from Cooper’s Ferry provided evidence that people were already present in Idaho before the corridor opened. This also raises the possibility that the initial human migration to the Americas followed a Pacific coastal route rather than through the opening of an inland ice-free corridor [3][2][10][8].