This is old San Diego Stadium, commonly known as Jack Murphy Stadium, and today as Qualcomm Stadium. Construction began in 1965 and completed in 1967. The San Diego Chargers of the AFL played their first game in the stadium that year. The minor league San Diego Padres of the Pacific Coast League played their final season there in 1968 and were replaced by the major league San Diego Padres in 1969.
Here’s another view of the stadium, this time from the air, while it was being constructed.
Source: David Valenzuela