Our knees just aren't what they used to be, but we still love the freedom and beauty of running on a surface that wasn't created by a steamroller. When we're not in the mood for the demanding ups and downs of some of the local single-track trails in desert parks, the dirt road leading west from the parking lot of Pima Canyon proves more than satisfying. A metal gate stops all motorized traffic from entering, but you may have to dodge a few fast-moving mountain bikes coming down the slope. And about that slope: It's gentle but relentless. It's just over a mile from the parking lot to the trailhead of National Trail, though the incline and uneven terrain makes it seem longer. Enough rocks and divots exist to force us to pay attention to the trail but that means it's working our muscles better than an ordinary jog would. Coming back, the grade isn't steep enough to punish our joints — much. We've used this two-mile-plus workout, done frequently over a multi-week period, to prime ourselves for the Grand Canyon, Humphreys Peak, and other hearty Arizona challenges.