The Humuʻula Groundwater Research Project researched the groundwater resources in the Hawaiʻi Island ‘Saddle’ region between Mauna Loa and Mauna Kea volcanoes by drilling two test holes. Resulting discoveries included: i) groundwater at a much shallower depth than expected, ii) a dike-impounded aquifer, and iii) a potential geothermal reservoir. This project collected a continuous sequence of rock core and made a complete stratigraphic record of the region. This continuous stratigraphic sequence contained subaerial shield-stage and post-shield-stage lava rock and ash samples from the Mauna Kea Volcano, documenting the area’s environmental, geologic, hydrologic, and thermal history.