For more than 150 years, ranchers in the West have gained insight about natural systems through daily interaction and management of landscapes, but this knowledge has never been systematically documented and analyzed. We interviewed 26 ranchers from a single watershed to understand how ranchers acquire their knowledge, document what they know about rangeland ecosystems, and explore how this knowledge varies within the ranching community. This exploratory study offers insight into the types of knowledge ranchers possess without attempting to survey all rancher knowledge or ascribe this set of knowledge to all ranchers. We identified three major knowledge categories in interviews: active knowledge applied to management decisions, embedded knowledge from living in place, and integrative knowledge that links ecological, economic, and social aspects of rangeland systems. We found rancher knowledge complemented scientific knowledge in its ability to provide site-specific information on management practices and ecological responses, and insight regarding potential indicators of rangeland health. Knowledge varies widely within the ranching community, and knowledgeable ranchers are readily identified through community referrals. Ranchers gained their knowledge primarily through experience and social interactions, and this knowledge is an untapped source of context-specific information. We did find that economic constraints, social norms, and proximity to the system might limit application of knowledge to practice. There is also a danger that this accumulated and dynamic knowledge base will be lost over the next generation, as many family ranches are sold to new ranchers or for nonranching uses. Based on our findings, we propose that more dialogue within ranching communities and between ranchers and scientists may lead to more sustainable land management practices and effective outreach efforts, and could expand and strengthen the informal social networks through which much rancher knowledge is shared and on which the social sustainability of ranching communities depends.