Off-Road Challenge

Go to the track selection screen and press the following buttons or
button combinations. If the codes are accepted, you should hear a
sound of an air wrench.

Unlock Guadalupe track
Hold Down and hit R. After, highlight the Vegas track, h
old Z and press the gas.

Unlock Flagstaff track
Hold Left and hit L. After, highlight the Mojave track,
hold Z and press the gas.

Unlock El Cajon track
Hold Up and hit L + R. After, highlight the El Paso track,
hold Z and press the gas.

Unlock extra trucks
Go to the vehicle selection screen and press the following buttons:

Truck - Button
4x4 Monster - C-Up
The Crusher - C-Right
Punisher - C-Down
Thunderbolt - C-Left