When the population of San Diego de Alcala Mission grew during the late 18th century, so did its demand for water. The Spanish colonists solved the water shortage problem by building what is likely the first major colonial irrigation-engineering project on the Pacific Coast. Known today as Old Mission Dam or Padre Dam, this National Historic Landmark collected water near the head of Mission Gorge on the San Diego River, and its five-mile-long aqueduct provided the mission with water for American Indians and Spanish colonists. Though damaged by floods, earthquakes, and human activity, the dam's stonewall continues to hold water. This impressive colonial ruin is a public site that visitors can enjoy within San Diego’s Mission Trails Regional Park.

The early years of colonization in Spanish California depended on the mission system. As Spanish colonists settled Upper California during the 18th century, they founded a chain of Catholic missions along the coast. This mission chain stretched north from present day San Diego to San Francisco. As in other Spanish colonies, the Californian missionaries’ goals were to convert American Indians to Catholicism, control the culture, and administer Spanish law. The southernmost mission in the California chain was San Diego de Alcala. Founded by Franciscan Father Junípero Serra in 1769, San Diego de Alcala was the first of 21 Spanish missions the Spanish established in Upper California.

Father Serra’s mission system laid the foundation for a European society on the Pacific Coast that opened California to Spanish, Mexican and later Anglo settlement. Before he sailed to Mexico in 1749 to spread Catholicism in the colonies, Father Serra lived a quiet life as a scholar and professor of theology. In Mexico, he established himself as a mission superior and in the 1760s, Spain chose him to set up a large mission field in California. Though Juan Rodríguez Cabrillo claimed California for the Spanish Empire in 1542, Spain did not move to permanently settle the area until Serra’s time. Serra, who traveled with soldiers and priests, arrived in California in 1769 and quickly established the San Diego de Alcala Mission. He went on to set up eight more California missions before he died in Monterey, California in 1784.

Father Junípero Serra Public domain image

At the turn of the 19th century, the mission fathers at San Diego de Alcala designed a dam on the San Diego River to supply their expanding community with water after it suffered a bad drought between 1800 and 1802. The mission’s Native American converts, who were from the Kumeyaay Nation, built the aqueduct and dam structures. The mission community started work on the dam after the drought in 1803 and completed construction of the larger irrigation system by 1817. When the laborers finished, the dam was 220 feet long, 12 feet high, and 13 feet thick.

The laborers used cobblestones, bricks, and cement for the dam wall, and they laid tiles on the bed of the long aqueduct to keep water from seeping into the sandy ground. The aqueduct, which ran from the dam to the mission, was two feet wide and five miles long. The community used the water to support its people, agriculture, and herds of cattle and sheep. After the secularization of the California missions in the 1830s, which followed Mexican independence, the dam fell into disrepair. By 1867, the dam and aqueduct were in ruins. In the 1870s, residents of the mission valley restored the dam. The historic dam still disrupts the flow of water in the San Diego River.

Old Mission Dam is part of San Diego’s Mission Trails Regional Park, an urban park northeast of central San Diego. The park preserves the natural landscape and visitors can enjoy its hiking and bike trails, a day-use campground, and Lake Murray Reservoir. Restrooms and a picnic area are located close to the dam, and the park visitor center provides visitors with information about the natural and human histories of the land. The historic San Diego de Alcala Mission, a minor basilica and active parish, is also open to the public and a short drive from the dam.