The ascent from the Lower Trailhead around the hillside and then along the creek upstream for three miles to the Upper Trailhead is gentle but there is little shade, so it's a good idea to bring water and be prepared for desert conditions.
About 7 miles up 8th Street in the Foothills above Boise
http://www.tripleblaze.com/trail.php?c=3&i=8100