According to Steve, it's final issue is the December/January issue, which is on newsstands now.
I've had a great time not only reading, but also contributing to, Adventure over the years, and my heart goes out to Steve, founding Editor John Rasmus, and all the others affected by the closing.
Steve put it quite well at the end of his post:
For those of you who are just passing readers of the magazine, its demise might be a mere curiosity or random note of economic discord. But for those of us who care about good writing, great photography, insight and curiosity and advocacy for an engaged relationship with the world at large, it is a truly remorseful day. The outdoor culture is far emptier for this news. Magazines are, of course, businesses, and some of them are nakedly commercial. But some are built around an idea or a calling, and these, the best of them, can create an emotional bond with their readership based on shared philosophy, common passion, and mutual respect. National Geographic Adventure’s tagline, “Dream It. Plan It. Do It.”, is a powerful call to action. More critically, it puts the focus on the reader, where it should be, to get up, get out, and get going. If past experience is any guide, those of us who have been connected to National Geographic Adventure, either as readers, contributors, or both, will carry fragments of that DNA with us, whether we’re writing, shooting photos, or simply out in the world. The magazine might not have survived this economy, but its ideals will. And for that, we should be thankful.