Those early 1900's low-tech hydrologists were amazing! The Tuolumne River at Hetch Hetchy matches the Merced River at Happy Isles at a surprising level of detail (with a linear transform). Observational error is exceedingly small (and even less than the residual, or observed minus simulated, discharge because the two basins are a close but not an exact match). This tight relation can be exploited both ways; to extend the 1916 Merced record back to 1911 (not shown) or to generate a forward "pristine" Tuolumne discharge record to compare with the post 1924 Hetch Hetchy Reservoir record. How strong is the correlation in spring daily discharge across the Sierra at high elevations?