There are low fares with several online travel agencies for Los Angeles to Paris at $453 to $473 round trip. Ticket prices are $300 higher on AA and BA websites and Google Flights does not show these fares. San Francisco to Paris prices as low as $535 in my searches.
Departure dates are January to May 2017.
SkyScanner.com search: American Airlines / British Airways
Los Angeles LAX – Dallas DFW – Paris CDG / Paris ORY – London LHR – LAX
$452.66 round trip ExploreTrip.com Sat Feb 11 – Sun Feb 19
This itinerary arrives in Paris CDG on the north side of the city and departs from Paris ORY on south side of city. Transportation is easy to both airports.
Momondo.com search: American Airlines / British Airways
San Francisco SFO – Chicago ORD – Paris CDG – London LHR (overnight) – SFO
$534.98 round trip ExploreTrip.com Wed Apr 5 – Sun Apr 16