The most feared and, per the Spanish observer Gonzalo de las Casas, 'the bravest, most warlike, treacherous and destructive of all the Chichimecas' -- a Chichimeca confederation centered on the Guanajuato sierras that fought the Chichimeca War from its opening years, faded from the documentary record after 1572, and was absorbed into New Spain's mestizo/Indian frontier society well before the war's formal 1590s end.
Took an active part in the Chichimeca War from its start (1550s-1560s raids on San Miguel de Allende, the 1563 'rebelión guamare' that destroyed Pénjamo, and the 1569 attack on El Robledal and Jilotepec, where they were defeated by Pedro de Ahumada Sámano). Unlike the Guachichiles and Zacatecos, who fought on into the 1590s, the Guamares specifically 'fell into decline' after the 1560s; per anthropologist David Frye (cited via indigenousmexico.org, sourced ultimately to Frye's chapter 'The Native Peoples of Northeastern Mexico' in The Cambridge History of the Native Peoples of the Americas, 2000), 'the last documented reference to them dates from around 1572, after which they apparently assimilated alongside the civilized Indians that moved into their region.' The Wikibooks Chichimeca overview independently corroborates that 'virtually nothing is known about the peoples referred to as Guachichiles, Caxcanes, Zacatecos, Tecuexes, or Guamares' post-war, in explicit contrast to peoples (Otomi, Chichimeca Jonaz, Pames, etc.) who 'maintain a separate identity into the present day.' Guamare is NOT a living people -- it does not continue and should NOT get a non-terminal fate.
The foundational scholarly monograph on the Chichimeca War; both the English and Spanish Wikipedia articles on the Guamares/Confederación guamare cite it directly, and it is the source behind the Gonzalo de las Casas quotes used across every secondary account of Guamare behavior. Verified as a real book via Open Library.
Frye is the anthropologist/historian whose scholarship (via his later Cambridge History chapter) underlies the '1572 last reference' claim used for this record's end_year; this monograph covers the same Chichimeca-descended frontier society (the Tlaxcalan-refounded town of Mexquitic, San Luis Potosí) and is the standard secondary source for how Chichimeca ethnic identities dissolved into colonial Indian/mestizo society after the war.
Already used as essential era context for the umbrella 'chichimeca' record in canonical data (ISBN 9780300140682); covers the 'peace by purchase' resolution of the 1590s that the Guamares' own decline (1560s-1572) preceded.