JD’s about to turn 12. His hardcore hiking days are nearly done. It won’t be long before his old bones can’t take the pounding, before he feels an unfamiliar twinge in those Jack Russell sinews signaling the end of his time on the trail.

If it’s any consolation, my old friend, I’m headed in the same direction.

I don’t take JD out for the companionship; I’ve been hiking solo all my life. Fact is, his need for water breaks and sniffing excursions slows me down. On hot days he’ll drag me over to a shady spot and sprawl for a couple minutes, his tongue protruding past his canines like a lurid pink gangplank.

I don’t take him for the primal vibe. Were the urge to grab a spear and take a domesticated hunting companion out to catch the scent of a saber-toothed tiger in my mental cards, the jangling of tags on JD’s collar would tend to dispel the reverie.

I take him because he loves going … anywhere.

Time was when JD’d scramble out of the car at the trailhead, clamp the leash with his teeth, shake it till his head nearly popped off, and scamper away with a growl and a grin. I was happy to indulge his Alpha philosophy: Life is like a dogsled team. If you ain’t in the lead, the scenery never changes.

But when I took him to Mt. Diablo last week, he exited the vehicle like a former Olympic gymnast – from the Rome games in ’60. He stuck the landing with remarkable grace for his age but didn’t earn any medals. He hit the trailhead at a trot, not the reckless gallop of his prime. Secretariat put out to pasture.

We hopped off-trail and trudged up a formation I call Meteor Hill. A few years ago he’d give me that “are we there yet?” look after three miles. Now it’s a mile. The first hint he’s done for the day: he falls behind. Oh, he can keep up; he’s simply suggesting a different direction – back. I stop to savor the scenery and he starts retracing our steps. Then his tether runs out. Sorry, Jack. Your pack leader isn’t ready to pack it in just yet.

One reason I choose off-trail routes is JD’s paws. Make that four reasons. Like the tread on old tires, his pads are wearing down. Grass goes easier on those aging tootsies than the hard dirt of the trail. Even a few years ago, when it became clear on our descent from Eagle Peak that his feet were killing him, I portaged him over the rocky passages like a kayak over sandbars – and gave thanks he wasn’t a 70-pound Lab. Now, as the canine equivalent of me at 80, he’d be hard-pressed to pull off Eagle Peak in the first place.

Once upon a time, a hike with the hound required extra vigilance. A ground squirrel would scurry across the trail and JD’d be after him like a heat-seeking missile. He’d also be a handful when we’d run across another dog – straining at the leash, ignoring my reasoned directives. It was hard to blame him. Were I the domesticated minion of a more intelligent being (and what married man isn’t?) and spotted another human on the trail, I’d go bonkers, too.

But now JD’s as mellow as Grandpa out for a round of golf. I watch his ears flop merrily along and feel a pang of sadness. Since the first canine was domesticated some 14,000 years ago, our dogs have become so intricately intertwined with us that they’ve lost their beasthood. Condemned to the limbo between their ancestors and their tamers, they can’t fend for themselves in the wild; can’t open a can of Alpo.

And yet … something about JD strikes the wild chord. “One does not meet oneself until one catches the reflection from an eye other than human,” wrote Loren Eiseley. My old hound might lack the wariness of the coyote and the lethality of the cougar. He might lack the self-sufficiency of every creature giving us a wide berth in the wild places. He might lack the jauntiness of his youth. What he radiates in abundance is abandonment to the moment, total immersion in every sight, sound and scent in that realm I visit, at times, in a haze of human awareness that my tether is running out, too.

I watch him bob and weave up the trail, head down, and wonder what scents he’s catching. Boasting 25 times my olfactory receptors, he could teach me a thing or two about East County ecosystems. Suddenly he stops, cocks his head and lifts a paw. He doesn’t seem to be looking anywhere; just listening. His auditory reach extends to 45,000 Hz; mine to 23,000 at best.

In some ways – in the most meaningful ways – he’ll always be a better hiker than his master.

Maybe that’s why, when I first pull out the leash and utter the incantatory “outside,” he still whines, yaps and whirls like a dervish. He has no vision of the ordeal ahead; no grasp of his mortality. His imagination extends to memories of sights, sounds and scents – and days in the sun with another old dog.