Figure 21. Geologic map showing outcrop of Ojo Alamo Sandstone in southeastern San Juan Basin (Figure 3). Mesa Portales study area contains paleomagnetic section across Cretaceous-Tertiary boundary and multiple USGS paleobotany localities through the same strata. OA-1, OA-2, KF, and N-1, N-2 (southwest and northeast of Cuba) are palynologic-collection localities of Anderson (1960). D6878, D3803, and D6582 are USGS paleobotany localities; palynomorphs from these sites are listed in Appendix. Geology west of long. 107 W. and south of the northern boundary of T. 20 N. from Fassett (1966); geology for the rest of area from Baltz (1967).