Landsat Thematic Mapper (TM) and SPOT panchromatic data were analysed to determine the lateral variation of the sedimentary and volcanic formations within and surrounding the Petrified Forest National Park in northeastern Arizona. Detailed geological mapping of portions of Petrified Forest National Park allowed for a correlation between TM images and the geological formations that aided in identifying these formations in unmapped areas outside and inside the park. A variety of image processing techniques, including band ratios, RGB composite images, selective principal component analysis and Brovey transformations were used in distinguishing these geological formations. Newly determined regions of the Lower and Upper parts of the Petrified Forest Member of the Chinle Formation were identified south of Pilot Rock and east of the Blue Mesa region. A final spectral reflectance-based geological map created by a maximum likelihood supervised classification algorithm provides a first-order approximation to the location of numerous sedimentary and volcanic units within and surrounding Petrified Forest National Park.