San Diego half dollars were struck at the San Francisco Mint in 1935 and the Denver Mint in 1936. They were struck to commemorate the "California-Pacific International Exposition, held in San Diego in 1935 and 1936. They were sold at the Exposition for $1 per coin. For the 1935-S San Diego there were 70,132 coins distributed. But actually, only about half reached public hands and some 30,000 pieces were retained by a few individuals associated with the Exposition. Seveal hoards were disbursed in the 1970s and 1980s. In the 1990s, approximately 5000 1935-S and 5000 1936-D San Diegos were sold into the market. Bottom line: the San Diego is a "hoard coin". In fact, PCGS has graded more 1935-S San Diegos (over 10,000 pieces) than any other silver commemorative of the 1892 to 1954 classic commemorative era.
The typical 1935-S San Diego is a frosty white Gem MS65. There are also several thousand MS64s and over a 1000 PCGS graded MS66s. This is a coin that is readily available in Gem condition.