@misc{indiciae2107b25cd330,
  title = {Quaternary geology of Contra Costa County, and surrounding parts of Alameda, Marin, Sonoma, Solano, Sacramento, and San Joaquin counties, California: a digital database},
  author = {E. J. Helley and R. W. Graymer},
  year = {1997},
  doi = {10.3133/ofr9798},
  url = {https://pubs.usgs.gov/publication/ofr9798},
  note = {Source identifier: ofr9798}
}