In this paper, we describe a core system for autonomous navigation in outdoor natural terrain. The system consists of three parts: a perception module that processes range images to identify untraversable regions of the terrain, a local map management module that maintains a representation of the environment in the vicinity of the vehicle, and a planning module that issues commands to the vehicle controller. We illustrate our approach by an experiment in which a vehicle travelled autonomously far one kilometer through unmapped cross-country terrain.