Lory encompasses 2,492 acres along the Rocky Mountain foothills in north-central Colorado. Precambrian rocks, mostly pegmatite, granodiorite, tonalite and metasedimentary rocks underlay the park and are exposed over the western two-thirds.
Exposed sedimentary formations include Pennsylvanian and Permian sedimentary rocks lying directly on Precambrian granites and schists creating a pattern along the east side of the Front Range. Stream courses have carved into the sedimentary rocks, creating steep canyons which drain mountain runoff. Sedimentary rocks are also exposed in bands parallel to the western Horsetooth Reservoir shoreline; these include the red siltstone and sandstone Satanka Formation and red calcareous sandstone of the Ingleside Formation.
Fountain Formation conglomerates and sandstones are also present in the vicinity of the reservoir. Metasedimentary rocks lie in east- to west-oriented, roughly parallel bands throughout the park. Tonalite is exposed south of Mill Creek, as is a band of Boulder Creek granodiorite. Pegmatite is exposed on the south-central park boundary. Colluvial deposits can be observed below the Fountain Formation and along Soldier Creek.