Sketch J No. 6 Showing the Progress of the Survey of San Francisco Bay and Vicinity Section X 1850 to 1853

This map has two Triangulation progress survey charts on one sheet. One chart is of the Bay of San Diego from the U.S. boundary line, to Point Loma and the interior of Bay of San Diego. Shows many base stations, points and astronomical stations. The second chart is a Triangulation progress survey chart of the Bay of San Francisco from Farallon Islands into the bay. Shows many base stations, points and astronomical stations. IMPORTANT NOTE: All of our United States Coast Survey (USCS), United States Coast & Geodetic Survey (USC&GS), and similar maps and charts have been professionally unfolded and flattened using humidity baths, semi-permeable membrane, and drying blotter techniques. Most others you typically see on eBay have not been, and worse, are quickly and crudely unfolded for the low-quality photos you see. Unfolding these maps in that way is damaging and weakens them. Please be aware.