Long before the upper Arroyo Seco became the stage for hiking trails and freeway bridges, it was known by the Indigenous Gabrielino-Tongva people as Hahamongna—a name meaning “fruitful valley, flowing waters.” A thriving village is said to have once existed here, a theory supported by artifacts uncovered in nearby citrus groves during the late 1800s and early 1900s.

One of the most remarkable discoveries tied to this ancient place came in 1938, during the construction of the Sheldon Reservoir. Located along Arroyo Boulevard in Pasadena, just three blocks south of the iconic Devil’s Gate Dam, the site yielded an unexpected archaeological find (CA-LAN-26). As city workers dug into the earth, they uncovered the remains of 53 individuals—people who had lived and died long before California became a state, before missions and railroads, even before European ships first reached the Pacific coast.

Excavating The Prehistoric Cemetery At The Sheldon Reservoir Site

Excavations revealed two separate layers of human remains, both in poor condition due to the passage of time. Alongside the uppermost burials were large stone tools—such as grinding stones, bowls, and mortars—that had been intentionally broken. This practice, known as “killing” the objects, was part of a spiritual tradition meant to free the items’ spirits so they could accompany the deceased into the afterlife.

Typical Burial Lower Level

Near the burials, archaeologists found about ten stone cairns—markers that may have been part of the Gabrielino/Tongva “Mourning Ceremony,” a sacred ritual honoring the departed.

Photograph of cairns at the site, circa 1938. Credit: Autry Museum

Various artifacts found in the site, including obsidian and soapstone tools. House at the Autry.

The expansion of Sheldon Reservoir was completed in early 1939 and continues to support the needs of the local area. As part of the Sheldon project, the archaeological site excavated, and the land was incorporated into the reservoir’s footprint. Artifacts recovered during the excavation were transferred to the Southwest Museum, which is now part of the Autry Museum of the American West.

Hahamongna is more than a watershed park—it’s a quiet archive of human history. Beneath its trails and bridges are the traces of people who lived with the land, not apart from it. It’s a reminder that the history of this land stretches far beyond what we see today!

Resources:
“A Cemetery at the Sheldon Reservoir Site in Pasadena” in Five Prehistoric Archeological Sites in Los Angeles County, California by Edwin Francis Walker, Southwest Museum, 1952.