There are many places throughout the West that are named Rock Creek. There is a Rock Creek (or Rockcreek) in NW Oregon in Washington County, but it is not the location of the Rock Creek Mine. The treasure guide that lists it's location is incorrect.
Rock Creek was a popular stop on the Oregon Trail. It was located just West of the Idaho/Oregon border in Baker County, about 14 miles NW of Baker. There never was much of a community. I do not know the location of the Rock Creek Mines, but it is most likely further NW toward the Elkhorn Mountains. The areas around Baker City and Sumpter have been quite productive for the last 100 years, and there still are active claims in the area. Some prospecting with a metal detector could prove sucessful in the search for gold nuggets.