Geologic map of the southern Rio Grande rift (RGR)–Basin and Range Province transition. Map includes thermochronology data (Kelley and Chapin, 1997; Ricketts et al., 2016; Biddle et al., 2018; Gavel, 2019; Reade et al., 2020), global positioning system (GPS) data (Murray et al., 2019), reflection/refraction line (Averill, 2007; Averill and Miller, 2013), and magnetotelluric data recording bulk crustal conductance (Feucht et al., 2019). Thick dashed black line is the boundary of Mack (2004). Cross-hatched areas show deep basins of the RGR (Seager and Morgan, 1979). Blue lines show crustal thickness (km), and white lines show heat flow (mWm–2) (Keller et al., 1990). AFT—apatite fission-track; AHe—apatite (U-Th)/He; ZHe—zircon (U-Th)/He. Inset shows metamorphic core complexes in blue and different models for the RGR–Basin and Range Province boundary, as discussed in the text. BR—Basin and Range; CP—Colorado Plateau; GP—Great Plains; RM—Rocky Mountains.