Ball comes to rest in a "erroded dirt canyon type thing"

I was playing with my brother the other day, he doesn't play all that often anymore but he still shoots around an 8 or 9 index and tries to follow the rules. His ball came to rest in some desert landscape. When we got up to it, it was in something that looked like this:

We literally broke out the rule book because he thought it played as abnormal ground condition but wasn't 100% certain. We didn't come to a 100% conclusion but per time constraints but we played it as an abnormal ground condition and dropped the ball within one club length, no nearer to the hole. It kept rolling nearer to the hole so eventually he just placed it and hit it.

Was that the proper way to play that or was it a "play it as it lies or take an unplayable lie drop + a stroke" ?

That would not be unusual or abnormal in a course with a 'desert landscape'. So the Committee would have no reason to mark it as such.

Unless it is marked, then play it as it lies.  One of my local courses has areas like that all over the rough.  It sucks being in them but we just bite the bullet and swing away.

Ahh, I see now. We had read this clause and assumed it was the right play:

25-1 . Abnormal Ground Conditions

a . Interference

Interference by an abnormal ground condition occurs when a ball lies in or touches the condition or when the condition interferes with the player’s stance or the area of his intended swing . If the player’s ball lies on the putting green , interference also occurs if an abnormal ground condition on the putting green intervenes on his line of putt . Otherwise, intervention on the line of play is not, of itself, interference under this Rule.

But I see now that this lie would not qualify as an AGC.

Thanks.

Play it down and putt it out!