The original mission — Mission Puerto de la Purísima Concepción — was founded in October 1780, part of Spain's attempt to secure the overland route to California by establishing a permanent colonial presence at the Yuma Crossing. It lasted less than nine months. Spanish colonists who arrived with the mission brought livestock that grazed on Quechan agricultural fields. The gifts promised to Chief Palma — who had traveled to Mexico City and received the full ceremonial treatment of a diplomatic ally — arrived irregularly, if at all.

On July 17 and 18, 1781, the Quechan responded to the violation of the terms on which they had agreed to host the missions. Fathers Garcés and Barreneche were beaten to death. Fathers Díaz and Moreno were also killed. More than one hundred Spanish soldiers and settlers were killed or taken prisoner. The prisoners were held for months until Spain sent an expedition with trade goods to ransom them in 1782. The missions were not rebuilt. Spain's colonial project at the Yuma Crossing was finished.

Saint Thomas Yuma Indian Mission was dedicated in 1923, built to serve the Catholic community on the Fort Yuma Indian Reservation. The decision to design it as a replica of Mission Purísima Concepción — the mission the Quechan had destroyed — layered the new building with historical reference. Visitors to Saint Thomas are looking at a deliberate architectural echo of a church whose destruction marked one of the most consequential moments in the region's colonial history.

The mission serves the Quechan people and their neighbors, the community that descends from the people who killed the priests of the original mission. This is not irony so much as the long time scale of religious presence in the American Southwest — the same faith that arrived with colonialism continuing in the same place, adapted to serve rather than supplant the community it operates within.

California Historical Landmark number 350 commemorates both the original mission of 1780 and the events of 1781. The designation acknowledges that what happened here — the founding of the mission and its destruction — was historically significant in ways that go beyond the loss of a building.

The 1781 uprising effectively ended Spain's attempt to colonize the Colorado River interior through the mission system. The coastal missions of California continued, eventually extending from San Diego to Sonoma, but the attempt to replicate that system at the Yuma Crossing was abandoned after the Quechan demonstrated, decisively, that they would not accept colonial terms that destroyed their agricultural base and violated the agreements they had negotiated.

Father Garcés himself is a complicated historical figure — a genuinely remarkable traveler who had covered thousands of miles of the Southwest, who had reached the Grand Canyon and the San Joaquin Valley, who believed his relationships with indigenous communities were built on mutual respect. The terms of Spanish colonialism made that respect impossible to maintain.

Saint Thomas today operates as a functioning parish church on the Fort Yuma Indian Reservation, serving a community of approximately 4,000 enrolled Quechan tribal members and their neighbors. The building that replicates the architecture of a destroyed colonial mission is now a place of worship for the descendants of the people who destroyed it — a continuity of presence on land that has been Quechan for longer than the historical record goes back.

From the air, the mission is visible as part of the Fort Yuma complex, the church architecture distinct from the surrounding development on the reservation land that straddles the California-Arizona border at the Colorado River crossing. Below the church, the river flows — diminished now by dams and diversions, but still the same river that Garcés traveled and the Quechan have known for centuries.