1. Precambrian sequence in the Needle Mountains, Colorado (abstract);Barker;Geol. Soc. Am. Spec. Paper,1967
2. Precambrian chronology in the Needle Mountains, southwestern Colorado (abstract);Bickford;Geol. Soc. Am. Ann. Meeting Program,1967
3. Needle Mountains folio;Cross;U. S. Geol. Surv. Folio,1905
4. Edad del Precambrico “anterior” y de otras rocas del zocalo de la region de Caborca-Altar de la parte noroccidental del Estado de Sonora;Damon;Univ. Nac. Aut. Mex., Inst. Geol.,1962
5. Absolute age of Precambrian rocks in Wyoming and Montana, Geochronology of Rock Systems;Giletti;Ann. N. Y. Acad. Sci.,1961