Refer to the race's "monster" listing
The "default" subrace for each of the standard races in 3.x is named in the Monster Manual entries for the races, where the racial traits from the PHB are reprinted. From the SRD:
These subraces may have different names in specific campaign settings - for instance, in the Forgotten Realms, high elves are known as "Moon" or "silver" elves, and hill/mountain dwarves are "Shield" dwarves (though rock gnomes and lightfoot halflings retain the default name). The appearance of races may also vary between settings; FR's elves, for instance, are much taller than the standard elves described in the PHB, being of comparable height to humans.