Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_name_31 ( year_completed INTEGER, dam_type VARCHAR, impounded_body_of_water VARCHAR )

### Question ###
Which Year completed has a Dam type of concrete gravity, and an Impounded body of water of deep creek reservoir?

### Accurate SQL ###

SELECT MIN(year_completed) FROM table_name_31 WHERE dam_type = "concrete gravity" AND impounded_body_of_water = "deep creek reservoir"