Starting in 1966, five years after his bachelor's degree was completed, Hildreth worked as a seasonal
naturalist for the
National Park Service. That same year, he conducted research at
Muir Woods National Monument, and published a report on the history of the area. During his time with the Park Service, he had stints visiting
Death Valley and the
Olympic Mountains. His early research also helped solidify the scientific consensus that there is compositional
zoning of
magma reservoirs. In 2012, Hildreth and Fierstein published a report to commemorate the
centennial of the 1912 eruption of
Novarupta. The pair had also published research on other volcanoes within the park, including
Kaguyak Caldera. Their enduring partnership proved fruitful, with them both becoming vital to each other's research. Subsequent works by him helped establish a greater understanding of the Bishop Tuff and its origins. In the
Andes, his work made him a leading expert on the geology of
Laguna del Maule. At the time of his death in 2025, Hildreth was a staff member of the USGS
California Volcano Observatory and worked out of
Menlo Park, California. He again participated in a GSA field forum in 2009, in
Bishop, California, which was adapted into a special issue of
Lithosphere. In July 2016, Hildreth and Fierstein hosted an interpretive lecture and hike at
Devils Postpile National Monument.
Awards and honors At the May 1985 meeting of the
Geological Society of America, Hildreth was elected a
fellow of the society. In December 1985, he was awarded the (named for
Norman L. Bowen) of the
American Geophysical Union for his
geochemical and petrologic studies of the Bishop Tuff, Novarupta, and Yellowstone. Hildreth became a fellow of the union in January 1995. In 2004, Hildreth was awarded the
Thorarinsson Medal (named for
Sigurdur Thorarinsson) for his many contributions to volcanology, including eruptive and petrological studies at
Mount Baker and
Mount Adams in the
Cascade Range,
Mount Katmai in
Alaska, and the
Yellowstone Caldera; mapping of volcanic calderas in the Andes; and magmatic studies at Long Valley. The GSA awarded Hildreth and Fierstein the 2019 Florence Bascom Geologic Mapping Award (named for
Florence Bascom) for their mapping efforts at Adams, Baker, Katmai, Laguna del Maule, and Long Valley as well as the
Three Sisters,
Simcoe Mountains,
Pantelleria,
Quizapu–
Descabezado, and
Mammoth Mountain. == Personal life and death ==