Rare and early map of the Gold Region of the Sacramento Valley

This is one of the earliest (if not the very earliest) published map actually to name and note the California "Mining District". One of the rarest maps of the California gold region, this is one of two known examples (Wheat, Gold TI49). The map shows Ranchos in the Central Valley and along the American river has "Gold Region" on both sides. 

It seems probable that Larkin had a copy of the 1844 Bidwell map in his possession at the time of the discovery of gold. He then overwrote it with the "Mining District" and sent (or carried) the map to friends in Boston who had it lithographed and published. It was likely also that it was a small run, thus accounting for its present rarity.