A wallow is a basically a mud hole, usually in or around a mountain spring, that bulls "wallow" or role around in.
I've located a lot of wallows while hunting and scounting, and I always seem to find bulls in those areas, but I've yet to ever actually SEE a bull in the act of wallowing. I think it would be a cool thing to see.
Here in Arizona, they start about August, but I have seen them earlier. If you can find one in summer, try to keep it a secret. I have seen them stop using busy one's right when the hunters start snooping around.
One of the most important components of deciphering a new hunting area is distinguishing between the summer and winter ranges for the game that you plan to pursue. Without knowing this you cannot make reliable assumptions about where the game will be come opening day. Knowing these areas will allow you to take the current weather (as well as the past couple weeks) and apply that to the landscape and make an educated guess as to where you might find that big buck or bull.
There are a couple ways...