OverviewGrape Mountain is relatively close to Boise, yet seldom visited. It does have a road to the summit, but the road is gated. The surrounding terrain lends itself to cross-country hiking, so the road is optional.
Although Grape is close to Boise, it does take a long time to drive there. It is right across the water from the standard route on Mt. Heinen, so you can see Grape Mountain long before you start the climb. If you have a canoe, you could cut off almost an hour of driving. But add about 500' of gain.
The hike to the summit from the parking area is about 3.5 miles and gains about 1450'. Expect this to take 2-3 hours. The map, below, shows a good loop hike.
In the spring, you can expect wildflowers. There is little to no flowing water on the hike, and not much shade, so pack accordingly.
Getting ThereFrom Boise, take Highway 21 toward Idaho City. After the Mores Creek Bridge, take an immediate right turn on a good paved road and head for Spring Shores and Arrowrock Dam. After the dam, the road becomes one lane, bumpy, and very twisty along the reservoir. Once past the reservoir, you will drive along the beautiful Middle Fork of the Boise River. Cross the river on the Rattlesnake Bridge (the first opportunity to cross) and follow the (better) dirt road up Slide Gulch for about 5.25 miles over the pass and down into the Elk Meadows flats. Take a right on the obvious dirt road heading toward your objective and follow the drainage to the gate at the saddle, about a mile.
Note that during the winter the road up Slide Gulch may not be maintained and this is snow country.
CampingThere are several campgrounds along Arrowrock Reservoir and the Middle Fork, or you can stay at the tiny Twin Springs Resort (see links). YOu could also do some "dispersed camping" at many spots along the way, including at the parking spot.
External LinksTwin Springs Resort
Splattski trip report
SuperDave trip report
For additional information on this climb and other peaks in the area, please see Tom Lopez's excellent book, Idaho: A Climbing Guide