Possibly the first expedition of White men northwest from New Mexico as far as the La Plata Mountains Of today was the one led by Juan Maria de Rivera by order of Tomas Velez Gachupin, Governor of New Mexico, in the year Although Rivera's journal of the expedition has been lost, its content is partly known to us by its having been known and used by Dominguez and Esca lante, who seem to have followed it more or less closely as a guide on their expedition in 1776, referring here and there in their diary to places described by Rivera.