Detailed map showing Sacramento and points north, published in United States, Senate Executive Documents No. 47, 31st Congress, 1st Sess., 1850. Rept. of Sec. of War, “Topographical Memoir Accompanying Maps of the Sacramento Valley, &c….”
Derby accompanied Brigadier General Bennett Riley on a tour of the gold districts in the summer of 1849, and this map is the result. It thus one of the first California Gold Rush maps based on actual observation — and the accuracy and detail are evident.