Detailed stress measurements in three boreholes penetrating horizontally bedded Devonian siltstones, sandstones, and limestones above a prominent salt decollement in the Appalachian Plateau of western New York have revealed variations in horizontal stress magnitudes which correlate with lithologic and stratigraphic units in all wells. High differential stress levels (up to 20 MPa) were found in shales of very high clay content, contrary to the proposition that such materials have negligible long-term strength. Elastic modulus data show that stiffer beds generally host higher stress levels and suggest that sand/shale stress contrasts result in large part from elastic shortening of the section in response to regional ENE compression. No correlation between stress and Poisson's ratio was found. However, a major systematic drop in stress level within the generally massive shales, which occurs across a group of sand beds near the base of the Rhinestreet, formation appears to be of different origin. The stress offset corresponds to the top of a section which we conclude, on the basis of local and regional total strain data derived from chlorite fabric measurements, once hosted abnormally high pore pressures. The total strain data also suggest the entire section above the salt has been uniformly shortened during Alleghanian deformation of the Devonian section are proposed, both involving abnormal pore pressure development in the sub-Rhinestreet section in response to limited drainage of fluid. Drainage of this paleo-overpressure is the best available explanation of the stress offset, although an additional remnant component must also be present to satisfy the stress data precisely. ¿ American Geophysical Union 1989