Although I refer to this area as "City Creek," it is part of a network of trails. A hundred yards up the trail, the trail splits. Left and up takes you past a women's prison, so if you're into that... Right follows City Creek until you get to a dirt/gravel road that keeps going up. At one point, you can go left to Kinport Mt. and down the other side (fun). Or you can just explore on the numerous roads in the area. Few trees make for great views in all directions.
Near City Creek Park on the west side of Pocatello (near ISU), park at the LDS church and begin heading west on your bike.
http://www.singletracks.com/item.php?c=1&i=3478