“Because attrition, traveling company splits, combinations, and recombinations were so common to the overland emigrating experience, the matter of conveying advice, progress reports, and other newsworthy information to relatives, friends, and former traveling companions was extremely important. The ‘roadside telegraph’ which overlanders devised was a crude by surprisingly effective means of communication. Anyone wishing to leave a message wold write a short note and place it conspicuously alongside the trail so that those following behind would be certain not to pass it by . . . The notes were usually of two types, those written on paper and those inscribed on such things as trees, pieces of wood, rocks, and animal bones. . . .Even human skulls were used. With surfaces that had been smoothed and whitened by the elements, these skulls and bones were strikingly visible, especially when hung by a stick by the side of the trail. . . .
While ‘Bone Express’ messages . . . were found along the trail, at certain places so many notes accumulated that these locations came to be known as ‘prairie post offices.’ . . . Someone even carved the words ‘Post-office’ on a rocky ledge near Courthouse Rock . . . but primarily these primitive post offices were found at trial junctions where the road forked and overlanders had a choice of routes to follow.”