FIGURE 1. Comparison of age determination and magnetostratigraphic correlations advocated in this paper and those of Fassett (2009). The lithostratigraphy and vertebrate fossil assemblages in the southwestern San Juan Basin (right half of diagram) are after Sullivan and Lucas (2006). The magnetostratigraphic columns are those of the Hunter Wash-Barrel Spring Arroyo area, the one area in the San Juan Basin where extensive biostratigraphic and radioisotopic data exist with which to constrain the magnetostratigraphic correlations.