TY  - RPRT
TI  - Coal regions and fields of the United States in digital form
AU  - S.J. Tewalt
AU  - C.L. Oman
PY  - 1993
DO  - 10.3133/ofr93396
UR  - https://pubs.usgs.gov/publication/ofr93396
ID  - ofr93396
ER  -