“…We interpret the increase in 87 Sr/ 86 Sr ratios in carbonate samples from Lake Uinta at~53 Ma as the result of a large-scale reorganization of the lake's drainage system with new and substantial inflows from Lake Gosiute and the catchments of the Greater Green River Basin that eventually extended into the Challis Volcanic Field at~49 Ma (KentCorson et al, 2006;Carroll et al, 2008 Sr ratios of samples from the Laney Member of the Green River Formation (~50 Ma) in the Greater Green River Basin (~285 km from our sampled section over the Uinta Uplift) give a mean of 0.71245 ± 0.00014 (n = 22, p b 0.05) (Rhodes et al, 2002). The more radiogenic Sr isotope composition of these samples reflects the radiogenic composition of Sr in adjacent, craton-cored Laramide structures (e.g., cores of the Wind River, Granite, Owl Creek, Laramie and Sierra Madre Uplifts were exposed in the Eocene Carroll et al, 2006), where whole rock 87 Sr/ 86 Sr ratios can be in excess of 1.0 (Divis, 1977;Peterman and Hildreth, 1978;Zielinski et al, 1981;Mueller et al, 1985;Frost et al, 1998;Patel et al, 1999). Although the Uinta Uplift bounding the Uinta Basin to the north is also basement-cored, the east-trending axis of the range is beyond the southwestern margin of the Wyoming craton, so that basement rocks at the core of the Uinta Uplift are a mixture of sediments deposited during the Neoproterozoic accretion of terranes (Ball and Farmer, 1998;Condie et al, 2001;Nelson et al, 2002;Foster et al, 2006 Sr ratios to also be high during the later stages of Lake Uinta's lifespan, when braided streams flowing south from the Uinta Uplift deposited fluvial units along the northern margin of the lake (Anderson and Picard, 1972;Davis et al, in press .…”