The most numerous and most feared of the Chichimeca nations, whose mounted raids controlled the silver road out of Zacatecas until a 1590 'peace by purchase' ended four decades of war.
Pacified under the 1590 'peace by purchase' policy (gifts of food, tools, land, and livestock; Franciscan missions; resettlement alongside Tlaxcalan colonist families sent north in 1591), negotiated in part by the mixed Spanish-Guachichil captain Miguel Caldera. Most Guachichil were absorbed into mission and mixed settlements over subsequent decades; a Guachichil community is still officially recognized today in San Luis de la Paz, Guanajuato, by Mexico's National Institute of Indigenous Peoples.
The standard scholarly monograph on the Chichimeca War, OL18510443W) and cited as the key source in both the Spanish and English Wikipedia articles on the Guachichil. Could not extract a page-level quote directly — see could_not_verify.
Primary 16th-century Spanish source specifically describing the Chichimeca peoples, including the Guachichil, by a contemporary colonial administrator. Verified to exist via Open Library (work OL43870278W)
Recent, Guachichil-specific study of Franciscan missionization