Located in the rugged landscape of Mission Trails Regional Park is a stone structure that quietly tells one of San Diego’s earliest stories. More than 200 years ago, an ambitious engineering project was built along the San Diego River to capture water, support agriculture, and help sustain Mission San Diego de Alcalá. Today, Old Mission Dam remains one of the region’s most important reminders of the challenges involved in establishing the Spanish mission community and the ingenuity used to overcome them. … The stone structure was an ambitious undertaking for its time — and much of it still stands today.