From the Super Mario Wiki
Boo Valley is a course that has appeared in two Mario games: Mario Golf, for the Game Boy Color and Mario Golf for the Nintendo 64. The course is located in a valley inhabited by Boos, hence the name. The course is fairly large at 6,635 yards. Bunkers are rare and there are only two water hazards in the course. However, due to the number of cliffs, it is very easy to hit the ball out of bounds.