Several years ago, George Gehrels and Bill Dickinson from UofA went looking for detrital zircon signatures in Paleozoic units of the Cordillera. They sampled the Upper Triassic Chinle Formation and its apparent shelfal equivalent in central Nevada, largely for comparison, and found a very unexpected group of ~525 Ma zircons. Cambrian plutons (the inferred source) are non-existent in western North America, and so I joined the group to discover the source. We sampled and dated zircons from the basal Upper Triassic unit of the Dockum Group of northern Texas, called the Santa Rosa Sandstone, aided by Tom Lehman from Texas Tech. The Santa Rosa Sandstone had a source in the Amarillo-Wichita Uplift, where Cambrian plutons are abundant. Sure enough, the sandstone was full of Cambrian zircons. What was odd, however, was the presence of Permian and Devonian zircons, whose age exactly matched similar populations in the western Nevada sample of the Upper Triassic Chinle Formation. The odd coincidence of zircon populations suggested to us a through-going river that traversed southern and southwestern North America at least between Texas and Nevada.
The next phase of the work has been the source of frustration, mostly due to failures to obtain funding. Bill Dickinson and I have always thought it would be a great experiment to get zircons from every basal Upper Triassic sandstone (the Chinle/Dockum equivalents) and get an idea of how the topography of Late Triassic North America controlled the path of what was clearly a major river system. Likewise, sampling upsection, in younger, but still Upper Triassic, sedimentary strata, might give us an idea of how the topography changed over time. Already Tom Lehman and I have discovered a very specific Devonian signature to upper Dockum Group strata (which matches up with detrital muscovite Rb/Sr dates). I am quite convinced that with the right combination of smaller sources of funding a good deal of work can get done.
Riggs, N.R., Lehman, T.M., Gehrels, G.E., and Dickinson, W.R., 1996, Detrital zircon link between headwaters and terminus of the Upper Triassic Chinle-Dockum paleoriver system: Science, v. 273, p. 97-100.