 In the town of Elma , US 12 exits the highway at a diamond interchange . From there , the main highway continues east to Olympia as State Route 8 ( SR 8 ) , and US 12 heads southeast towards Oakville and Rochester . East of Oakville , US 12 runs north of the Chehalis Indian Reservation . It then continues east through the town of Rochester , and interchanges with I @-@ 5 at exit 88 in the town of Grand Mound . 
