This dataset was prepared by Brian Yellen, a research assistant professor in the Department of Earth, Geographic, and Climate Sciences at the University of Massachusetts Amherst. Dr. Yellen worked in conjunction with Melissa Grader of the USFWS and colleagues to conduct the associated field sampling. This report provides information related to the substrate grain size at surveyed locations on Rainbow Beach on the Connecticut River in Northampton, MA (42.322125, -72.584928). This location is a known breeding site of the endangered puritan tiger beetle (PTB), Ellipsoptera puritana.