I'm a certified couch-potato baby boomer from frozen Maine, whose exercise consists of turning pages or stoking fires. But when I visit my friend Barb in Tucson, she convinces me to join her tennis club for an outing in the mountains. "Of course you can do it," she cajoles. "Two of the gals are in their eighties." Driving north to the Santa Catalina Mountains, she explains that the Sonoran desert contains four of the six Life Zones.

Hiking Rose Canyon trail, five brutal miles long, we hit a heavily rooted section where loose stones threaten our footing. Next we inch up a sheer rock incline and clamber over gigantic fallen ponderosa pines. The sun climbs higher and so do we. STRAIGHT UP. The ten tennis ladies march along, politely ignoring my huffing, puffing and frequent stops. Since it's about 30 degrees cooler up here despite the fierce sun, I'm grateful for my light jacket. Atop Mt. Lemmon, we rest, peering at Tucson six thousand feet below, then retrace our steps.

Exhausted but happy on the drive back, I marvel at the sentinel-like, two-hundred-year-old saguaro, their crown of white flowers blooming in late spring. Mostly, though, I'm just vastly relieved that I managed to survive my daunting trek with these indefatigable tennis ladies.

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