Staring out across the lush and unforgiving landscape of China’s Yunnan and southwestern Sichuan Provinces with a geologic map in hand, one is immediately humbled by the skill of the Chinese geologists who were tasked with a seemingly impossible job. The mapping was, by and large, accurate; however, the Cenozoic chronology was based entirely on biostratigrapic and lithostratigrapic correlation (e.g., Ge and Li, 1999) with little, if any, absolute age control. With limited exposure and elusive datable horizons except for a few dikes cross-cutting stratigraphy and interbedded lava flows (e.g., Studnicki-Gizbert et al., 2008), there were few constraints on absolute time in the Cenozoic. Because the area is important for understanding the evolution of the Tibetan Plateau as a whole, the community working in the area pressed on, leaning heavily on the regional stratigraphy in building a Miocene history of how rivers re-organized and incised the Tibetan Plateau’s southeast margin (e.g., Clark et al., 2004; Schoenbohm et al., 2006) in response to passive surface uplift resulting from flow of the lower crust (Clark and Royden, 2000) (Fig. 1A). This narrative was reinforced by subsequent low-temperature thermochronology that yielded a middle Miocene timing of river incision (Clark et al., 2005; Ouimet et al., 2010). Using largely the same geologic age constraints from the sedimentary basins, paleo-altimetry studies determined that the Plateau margin was already high in the Eocene (Hoke et al., 2014; Li et al., 2015; Tang et al., 2017), consistent with high elevations in southern and central Tibet (Rowley and Currie, 2006).