If it's an American Bullfrog (Rana catesbeiana), it is not considered an invasive species in LA, although it is a non-native species introduced in the 1920s. Here is a map showing its current range.
http://en.wikipedia.org/wiki/File:Bullfrog_range.gif
It's range is mostly limited by high elevations and dry climates.
Here is a good California site about American Bullfrogs, with lots of pictures.
http://www.californiaherps.com/frogs...tesbeiana.html