surfaud.dat is a surface audio file located in the
...\data directory for San Andreas. It assigns audio to a collision when objects interact with the surfaces. The interactions include the footsteps peds make and vehicles sliding on the surface.
There are ten columns in each line. The first column is the name of the surface as defined in the surfinfo.dat. The rest of the columns are the audio data in the order as shown above. To assign an audio to a surface, place a "1" in the corresponding column. You can assign more than one audio for each surface to create unique sound effects like creating mud.