
More on the early surveys can be found here: https://pubs.usgs.gov/circ/1050/pdf/CIRC1050.pdf?utm_source=twitter&utm_medium=social&utm_term=71d2e8e7-ca66-42be-8e2e-884d17ed9d62&utm_content=&utm_campaign=usgs.
More on the early surveys can be found here: https://pubs.usgs.gov/circ/1050/pdf/CIRC1050.pdf?utm_source=twitter&utm_medium=social&utm_term=71d2e8e7-ca66-42be-8e2e-884d17ed9d62&utm_content=&utm_campaign=usgs.