TY  - RPRT
TI  - Preliminary bedrock geologic maps of the Westford and Billerica quadrangles, Middlesex County, Massachusetts
AU  - Donald Clayton Alvord
PY  - 1975
DO  - 10.3133/ofr75387
UR  - https://pubs.usgs.gov/publication/ofr75387
ID  - ofr75387
ER  -