CREATE TABLE table_name_31 (year_completed INT, dam_type VARCHAR, impounded_body_of_water VARCHAR)

Which Year completed has a Dam type of concrete gravity, and an Impounded body of water of deep creek reservoir?
SELECT MIN(year_completed) FROM table_name_31 WHERE dam_type = "concrete gravity" AND impounded_body_of_water = "deep creek reservoir"
SELECT MIN("year_completed") FROM "table_name_31" WHERE "concrete gravity" = "dam_type" AND "deep creek reservoir" = "impounded_body_of_water"