California and Nevada in 1871 - Virginia City, Sacramento, Carson City

The French mining engineer Edmond Guillemin-Tarayre compiled this geological map of California and Nevada in 1867, publishing it in Paris in 1871 as one of seventeen plates accompanying a scientific volume issued by France's Commission Scientifique du Mexique, the country's scientific mission that had originally traveled to Mexico under the shadow of its ill-fated attempt at establishing an empire there. The map is almost certainly the first geological map of California and Nevada published anywhere in Europe, portraying ten distinct geological units through color lithography paired with letter symbols, a dual system that made correctly identifying each unit far easier than on most earlier American geologic maps. Guillemin-Tarayre drew on the investigations of the Pacific Railroad surveys and California's own Whitney Survey alongside his own fieldwork, and later geologists rated the resulting interpretation as more accurate than any geologic map of California produced before it, a distinction it held for several years after publication despite having been buried for decades in an obscure French volume that historians only rediscovered relatively recently.

The Comstock Lode anchors the map's Nevada coverage, the silver discovery near Virginia City that in 1859 had touched off the rush of miners, loggers, and traders whose sudden arrival necessitated a new railroad through the Washoe Valley connecting Virginia City to Truckee. The Sierra Nevada gold veins receive extended treatment on the accompanying text and map together, the mountain range whose mining districts the volume's geology chapters return to repeatedly. Towns, rivers, and lakes are identified in detail across the base map beneath the geological overlay, along with county names, even though the map does not attempt to draw county boundaries themselves. The southeastern corner of California falls outside the map's border, the one significant gap in an otherwise remarkably comprehensive treatment of the state's geology for its time.

This map is a striking choice for a California or Nevada family with ties to the Comstock-era mining boom, someone drawn to the Virginia City and Washoe Valley story specifically, or a collector interested in rare, scientifically rigorous French cartography of the American West. The Vault also carries this same French mission's companion base map and metallurgic map of the region; where those sheets emphasize geography and mineral resources respectively, this geological plate is distinguished by its detailed ten-unit color-coded rock classification, the most technically ambitious of the three. It's available unframed in a full range of sizes, from a compact study print to a larger statement piece.