Somewhere in the information on the first page it should say that the trip is 8 miles long round trip. From reading the description it seems as though once you've reached the parking lot, you are there. I found information about the hike itself from another site.
If you need fuel or supplies, please note that Kenton is not a town. It is a "census designated place," and has no services other than a B&B or two. The nearest gas and grocery is 35mi away in Boise City (pronounced "boys" rather than "boy-see").