Just look how hard it was for Haley to get information on Tyrania or whatever the name of that country was. Actually she didn't get the information. And that was just 5 years or so ago.

Now imagine trying to get information on some place in the middle of the desert that no one even cares about that might have changed it's name 40 times by then.

Also it's possible the gate is not even in the canyon, that that's just where the Draketooth HQ is. The gate might be somewhat outside.

Or... you know. Wizard. Epic. Even if Girard was an Illusionist he still has tons of "normal" wizard spells he can prepare when he has to. Maybe that canyon wasn't there before and he made it.

That way when Soon would swing by he'd say "No, we don't have to search here, the gate wasn't near any canyon".