Río San Gregorio, locally known as the Río San Gregorio (Ávalos), is a mountain river in the Córdoba province of Argentina that flows from its headwaters down through rugged sierra terrain until it meets the Río Quilpo. Situated at elevations ranging between 1,000 and 2,000 meters above sea level, this river runs cold and clear through the mountain slopes of the Sierras de Córdoba, making it a classic destination for fly fishing enthusiasts. The river's pristine, transparent water and mountain character give it the feel of a true sierra trout stream, and its relative remoteness contributes to a quality angling experience in a stunning natural setting.