Cressman was a systematic and productive researcher who worked across a wide range of Great Basin sites, documenting the archaeological record of a region that had received little systematic attention before his work.

Cressman recovered evidence of human occupation at the Paisley Caves from layers that he and his colleagues argued were geologically old.

He found artifacts and other evidence of human presence, and he argued that some of this evidence was from the Pleistocene period — a claim that, in the academic climate of the mid-twentieth century, was viewed with considerable caution by many of his colleagues in the field.

The specific nature of the evidence Cressman found, and the arguments he made about its age, are worth understanding as context for the later DNA research.