Data behind Powell's Uinta Mountain Report: The 1871 Contributions of F.M Bishop and John Steward

The quality of observation, both for mapping and geologic interpretation, can be evaluated for Powell's 1871 Green River expedition. Although many writers dismiss Powell's crew as amateurs, primary documents show that two members of the party, F.M. Bishop and John Steward, were sophisticated observers and careful interpreters of the topography and geology.

Bishop was the assistant topographer and maintained the composite map; his mapping was used by Powell in the atlas accompanying the Uinta Mountain report. Where astronomical observations could be made, latitudes were very accurate. Longitude errors were greater, but the largest errors in open country correspond to an error in measuring local noon by 30 seconds (time); both reading the chronometer and measuring solar elevation or the due south position contribute to this error. Where it was not possible to make astronomical measurements (such as within canyons), the mapping is less accurate. Some combination of approximating stream velocity and dead reckoning produce a map on which major features can be identified, but positional accuracy is lacking.

Steward's geologic observations were of high quality, even if some of his interpretations were later revised. At Browns Park he accurately noted the lithologic characteristics and the angular discordance of the units but failed to understand the ages of the units, interpreting the depositional history in terms of Pleistocene glacial processes rather than as Tertiary age terrestrial deposition. From Echo {park to Split Mountain, he accurately describes and sketches the Mitten Fault, the Rainbow Park syncline, and the Split Mountain anticline. His sketch of the complex structure just south and west of Echo Park conforms to the modern accepted mapping. The detail of Steward's notes and structural analysis were inconsistent with the scale of the final Uinta Report, so Steward's observations were lost to the geologic community when Powell's notes were archived.