Any information about the Jacaranda trees in downtown San Diego,
especially what year they were planted and where did the stock come
from.

The City of San Diego's website credits Kate O. Sessions "with
popularizing the jacaranda and Brazilian pepper trees as well as
poinsettias and birds of paradise in San Diego" beginning around 1892.

http://www.sannet.gov/park-and-recreation/parks/balbgard.shtml

Thanks Infomatron-ga. I was aware of this. 
I have a bet with someone about the actual year the trees were planted
in downtown San Diego, since I do not remember seeing them in the
50's. Perhaps they were very young and inobtrusive. Incidentally, it
is an amazing thing to look down on the entire San Diego area from an
airplane in the month of May and see the spectacular array of
lavender/violet jacarandas.