In the 2000 census, the 51st District was renumbered the 50th District. The district was gerrymandered to exclude the relatively liberal areas of La Jolla, Bird Rock, downtown La Jolla, and UCSD. Those areas were moved to the more-liberal 53rd District, and the more conservative community of Clairemont Mesa was added to the new 50th District.
source.
SD Tribune says that of the 350,000 registered voters, 157,000 are Republicans, 105,000 are Democrats and 76,000 are independents.