This report presents new fission-track ages for Tertiary volcanic rocks in the Mogollon plateau, southwestern NM. A sample of Nabours Mountain Quartz Latite taken from Mogollon Mountains, sec 22, T11S, R19W, Catron Co, NM, in Basin-and-Range province, produced a fission-track date on sphene of 27.5 +/-0.7 m.y. This date suggests that the development of the Bursum cauldron (with which Nabours Mountain is related) was completed in a relatively short time. Apache Spring Quartz Latite--the first eruption associated with the Bursum cauldron--erupted at 27.3 +/-0.8 m.y.; Nabours Mountain Quartz Latite--the last recognizable eruption associated with the cauldron--erupted at 27.5 +/-0.7 m.y.

Source: GNU records (USGS DDS-6; Denver GNULEX).

Is a flow-banded rhyolite in the western and central Mogollon-Datil volcanic field, Catron Co, NM, Basin-and-Range province. Has yielded ages of 28.3 +/-3.9 m.y. (sphene) and 28.4 +/-0.8 m.y. (sanidine). [These ages are generally regarded as Oligocene.]

Source: GNU records (USGS DDS-6; Denver GNULEX).