biotite yielded 25.7 million years. This pulse of magmatism at about 25 million years may have been accompanied by uplift of the Defiance-Chuska high in addition to the uplift during the Laramide orogeny. Helium-rich gas has been extracted from Devonian strata in the Dineh-bi-Keyah field. Additional economic resources have included uranium, mined from some of the Mesozoic strata, particularly from the Morrison Formation in the Lukachukai Mountains at the northwest end of the Chuska Mountains. References Lucas, Spencer G., Semken, Steven C., Berglof, William R., and Dana S. Ulmer-Scholle (editors), Geology of the Zuni Plateau, New Mexico Geological Society Fifty-fourth Annual Field Conference, 424 p., 2003. Brand, B. D., Clarke, A. B., and Semken, S., 2008, Eruptive conditions and depositional processes of Narbona Pass Maar volcano, Navajo volcanic field, Navajo Nation, New Mexico (USA). Bulletin Volcanol. Steven M. Cather, Lisa Peters, Nelia W. Dunbar, and William C. McIntosh, Genetic Stratigraphy, Provenance, and New Age Constraints for the Chuska Sandstone (Upper Eocene-Lower Oligocene), New Mexico–Arizona. in Lucas et al., cited above, pp. 397–412. Steven M. Cather, The Chuska erg: Paleogeomorphic and Paleoclimatic implications of an Oligocene sand sea on the Colorado Plateau, Four Corners Geological Society News Letter, February 2007 (accessed May, 2007), http://www.fourcornersgeologicalsociety.org/ Steven M. Cather, Sean D. Connell, Richard M. Chamberlin, William C. McIntosh, Glen E. Jones, Andre R. Potochnik, Spencer G. Lucas, and Peggy S. Johnson, The Chuska erg: Paleogeomorphic and paleoclimtic implications of an Oligocene sand sea on te Colorado Plateau. Geological Society of America Bulletin, v. 120, pp. 3–33, 2008. Nathan B. English, Julio L. Betancourt, Jeffrey S. Dean, and Jay Quade, "Strontium isotopes reveal distant sources of architectural timber in Chaco Canyon, New Mexico." Proceedings National Academy of Sciences USA'' 98, 11891–96, 2001. Colorado Plateau Mountain ranges of Arizona Mountain ranges of New Mexico Mountain ranges of Apache County, Arizona Geography of the Navajo Nation Landforms of San Juan County, New Mexico