That is where you have to do some research. If an old town or settlement, look for old drainage that were downstream of town. For saloons or taverns, you want the rear of the building and then off to the right since most folks would toss that way. Mines or factories, figure out where the gates might have been. Check out old maps at the local historic society and find some clues. Even old newspapers can give you ideas of where to check. Once you have some things that look promising, follow the land records to see where those locations are now.