Most Angelenos can go a lifetime without knowing the hiking possibilities in the San Gabriel Mountains, several just a speedy zip up the Glendale Freeway. The San Gabriels are real mountains, considerably taller than the East Coast's tallest peaks, but hikes often begin in the relatively gentle, lower foothills, so don't let fantasies of a 6,000-foot vert scare you away. Lower Arroyo Seco begins with a flat, lightly winding road or path turning into an increasingly graded romp through pleasantly forested terrain, featuring deciduous trees that lend a surprisingly northern feel. You'll also cross a rushing brook that turns into a small river in snow-melt season. The beginning of the hike passes the canyon inhabited by the aeronautics installation JPL (Jet Propulsion Laboratories). Beware, however: You can look at the lab, but don't take ultrazoom photos or you may be hounded by helicopters and unmarked cars like the kid in Eagle Eye. Parking lot at North Windsor Ave. near Mountain View St., Altadena.