There are two things you need to know about this hike, and they're both supercool: 1) the Alta Trail is situated on the front range at South Mountain Park, and we're betting that many of you didn't even know there was a front range; 2) the "Alt" section of this trail is not maintained and does not appear on any of the park's maps. Translation: It's not choked with other hikers and it's completely badass.
If you want to hike the "official" Alta Trail, drive about two miles down the San Juan Road and park in a gravel lot at mile marker 2.5 and the Bajada Trailhead, where you connect with a well-maintained trail to the top. That's fine, but you'll miss most of the eastern section of the range and a helluva lot of stellar trekking if you choose that route. Better to do it our way.
After you pass through the headquarters section on the park's main road, turn right at the sign that says Big Ramada and Little Ramada picnic areas. Drive as far as the road will take you and then park. Aim for the nearest rise to the west, and follow the dirt tracks that lead inexorably to the summit of the range. After a brief but leg-frying up, you'll find yourself atop a panorama-saturated, dragon-back ridge that follows the crest of the range all the way to its terminus at San Juan Lookout, about four miles away.
When you get to San Juan, turn around and do it in reverse.
You'll regret it — but you won't.