In Boca Negra Canyon along the Cliff Base Trail, petroglyphs were placed deliberately according to each boulder's orientation to the sun and the surrounding landscape. Some boulders have petroglyphs on east-facing sides, while others bear petroglyphs on all sides. Atop the large boulder to the right is a grinding surface as well as several petroglyphs. These archeological features were used for sharpening stone tools, grinding corn and seeds, making pigments, or preparing plants as medicines.