TY  - RPRT
TI  - Preliminary geologic map, District of Columbia
AU  - A.J. Froelich
AU  - John Tilton Hack
PY  - 1975
DO  - 10.3133/ofr75537
UR  - https://pubs.usgs.gov/publication/ofr75537
ID  - ofr75537
ER  -