In 1861 Mark Twain visited Lake Tahoe and staked a timber claim. While at the lake he camped at the lake shore and found a rock to use as a desk to write to his mother and play the card game Faro. From the description Twain gave in "Roughing It" and a little research and looking I think this is the rock.
Cache is up the slope from the rock and the picture was taken from the cache location.