Start at the junkyard on Nelson Way and drive south to eventually end up at an opening to your right. This is the Paradise City Airfield. It has the barrel roll jumps and a difficult double super jump.
At the main menu or while the game is paused, select "Under The Hood" > "Sponsor Code". Activate the following cheats by entering the corresponding case sensitive codes. The cars will appear in the junkyard after earning the required license. Sponsor codes do not work for the v1.6 and higher patches:
CHEAT FUNCTION - CHEAT CODE/LICENSE Circuit City Hotrod - Enter "circuitcity" and get the burnout paradise license. Hunter Best Buy Oval Champ car - Enter "bestbuy" and get the A license. Kitano GameStop Sport car - Enter "gamestop" and get the A license. Kitano Micromania Hydros Custom car (French version) - Enter "H211 1Z99 LZ00 00BB"(those are zeros) and get the A license. Steel Wheels car - Enter "U84D 3Y8K FY8Y 58N6", "E60J 8Z7T MS8L 51U6", "G23X 5K8Q GX2V 04B1", or "E165 6L1Q ZQ2H 10V3", and get the "Burnout Paradise" license. Steel Wheels car (European/Autralian version) - Enter "Z891 4K88 IN25 79AA" or "B179 8M20 XA09 80FF" in the European or Australian version of the game, and get the burnout paradise license. Wal-Mart F1 racer - Enter "walmart" and get the burnout paradise license.
To get to the secret quarry area, starting at the top part of the dam, head west and take W. Lake Drive northwest, and turn left. You will see an opening with a road that leads down and can be used to perform barrel rolls.
With the Kitano Hydros Techno, floor the gas and the brake, and the car still moves. Simply add boost to burn out at a very slow speed, making it easier to react to oncoming traffic and obstacles.
Switch to a speed boost-type car (preferably the Ubershall 8 because of the square front end or any speed car with one) and go to the gas station on Angus Wharf. This is the only station this trick will work at and it cannot be online because of the Cagney Update. Drive to the south end of the station, then drive and boost into the concrete triangle at the end of the station. Continue boosting and the game will think you are going through the station. You will keep getting boost refills after you Burnout. Keep holding and and if you start to lean towards one way turn in the other direction. After a few minutes you should hit Burnout x20.