Reaching the Old Mesa from the Glade in the Wilderness is a simple enough matter:
North (to reach empty node north of Glade in the Wilderness)
East (turns northeast, Old Mesa is a hidden location south of the path)
While from Thorn Ford you need to head:
Southwest (cross the river)
Southeast (along the river)
Southeast (along the river, again)
Southwest (Old Mesa is a hidden location south of this path)
When you arrive, head north, then northwest to find an abandoned camp - abandoned, that is, save for the Werewolf that now guards it. This Werewolf isn’t too dreadful a foe, but it does have one major strong point that may give you trouble: Damage Reduction.
Damage Reduction: Creatures with Damage Reduction ignore a set amount of damage from an attack, but fortunately most Damage Reduction can usually be overcome if the attack meets certain conditions. These conditions usually include being magical (attacking with a weapon that has an Enhancement bonus of +1 or higher), being made of a certain material (silver, for example), coming from a character of a particular alignment, or being the right damage type (slashing/piercing/bludgeoning). Damage Reduction is usually displayed by the number the damage is reduced/the condition that overcomes said Damage Reduction, such as DR 10/magic or DR 5/bludgeoning. Damage Reduction generally does not apply to damage dealt directly by spells.
In this case, the Werewolf likely has Damage Reduction 10/silver, or something similar. Whatever the exact resistance, chances are you have no means of overcoming it right now, so every attack you land will deal ten less damage. You can overcome this by using direct-damage dealing spells like Magic Missile to deal damage, or just by having warriors who can deal enough damage - Amiri is passable, and the odd critical hit and sneak attack will help out tremendously, as will using feats like Power Attack. The Werewolf isn’t a terribly powerful foe, nor one protected overly well by HP or Armor Class, but if your offense grinds to a halt against it, feel free to abandon this area and come back later.
That all said, most parties should have a character capable of dealing significant damage to the Werewolf, so it’s rather expected you’ll be able to take down this beast. If you buff your tank with Blur and Shield of Faith it’ll take the Werewolf that much longer to cause trouble, giving you plenty of time to swing for those critical hits.
When it dies, loot its corpse for a Breastplate +1, a Potion of Invisibility and a Ruby, the latter of which will sell for a cool 750 GP, then loot a nearby chest for a Potion of Vanish. Further rewards can be found to the north, where a corpse will yield a Potion of Reduce Person and some baubles.