Justin Bieber Races Downhill with Model Gal Pal

Justin Bieber is in a race to the bottom ... but at least now he's got some attractive company.

Bieber took a 1-on-1 hike with his model friend, Ashley Moore, who seemed down to get physical with him in a friendly competition running on a canyon trail.

If there's one thing we know about Bieber ... he tends to open up in the wilderness. Bodes well for Ashley. Plus they've hung out before -- couple years ago at a Clippers game -- so, seems like they've got a connection.