Why did Xiang Yu give Liu Bangba such a rich natural barrier? He didn't know or what?

Come on, Bashu was not rich at that time, but it was still a wilderness. There was a natural barrier, but Xiang Yu deliberately arranged him to that place, because the natural barrier was guarded by Xiang Yu's army! For example, it is like a tunnel. What would you do if you blocked the entrance and exit? After all, I have to guard against the crusade against Liu, so Han Xin will only sneak away in the future! Otherwise, who would be stupid enough to walk on a mountain road full of crisis, just because the road is blocked by Xiang Yu, can't get through!