The East Bay has more than a thousand miles of trails, many of them steep, but not all of them open to those with tails that wag -- unfortunate news for the myriad dogs who seek a good workout with their human companions. But the 6.1-mile Corduroy Hills loop in the Las Trampas Wilderness outside of San Ramon will leave both canine and human with stiff legs, sore feet, and an appetite for at least two days of sleep. To get the most out of this tough trail, go after a rainstorm, when the mud-to-trail ratio is high, allowing dogs maximum opportunities to romp and slide while waiting for their humans to huff up the hills. The loop begins on the Chamise Trail, which steeply switchbacks up before ending at the Las Trampas Ridge Trail. Follow that up to just east of 1,787-foot Vail Peak, and take a sharp right down the Corduroy Hills Trail. This portion offers welcome but short-lived downhill relief. Follow the wooden steps down to an open meadow and feel the wind in your ears. The route levels out, but not for long: Up you go again, followed by some knee-aching descents. At 2.5 miles, the Corduroy Hills Trail spills into the Madrone Trail. Follow this straight to a right turn on the Virgil Williams Trail, and another right on the Del Amigo Trail. Until now, the going has been rough, but this loop saves the toughest segments for the second half of your journey. This steepest part of the route offers views of Mount Diablo that humans will likely never see as they slog uphill. This section ends at a junction with the Summit Trail, heading up, and the deceptively flat Sulphur Springs Trail, which you will take right. But it, like the other trails in this loop, is not flat. Here, the dogs should cease their out-and-back romps to roll in cow pies and sniff for rabbits and remain at pace with their human companions. Shortly, the trail follows a creek -- good for splashing away the manure! -- before reaching the Trapline Trail, which leads back to Chamise Trail. A final steep descent ends your loop and gives you a newfound appreciation for the term dog-tired.