Kopera, J. P., DiNitto, R. G. & Hepburn, J. C. Bedrock geologic map of the Marlborough quadrangle, Massachusetts. geologic Map (2004).

Kopera, J. P. Preliminary bedrock geologic map of the Ayer quadrangle, Massachusetts. Open-File Report (2006). at <http://www.geo.umass.edu/stategeologist/>