We recently published a short video essay on the 1849 official map of San Francisco by William Eddy.
Perhaps the most striking feature of this map is the so-called Lagoon Survey grid located in the northwest corner of the map past Larkin St. In the video we discuss the mysteries surrounding the survey, as well as the few remnants of it still seen today. For more context, I recommend a recent article by Gary Kamiya in the San Francisco Chronicle.
Kamiya discusses the ecological and historical backdrop for the survey, an area called Spring Valley, through which ran a trail to the Presidio and where the freshwater Washerwoman's Lagoon was located.