The history of property mapping in California after it became a state in 1850 begins at the summit of Mount Diablo. The mountain’s prominence on the landscape made the summit the perfect location for early land surveyors to mark the starting point for a grid of lines that would be used to define property boundaries throughout most of northern California and all of Nevada. Surveying expert John Pettley will discuss the history and significance of the survey marks on top of Mount Diablo which are still in use by land surveyors today.