You examine the bridge you've been carrying around. It's not long enough to span the Orc Chasm, but it turns out it's of smut orc manufacture. How convenient!
You disassemble it into usable lumber and fasteners.
When approaching after collecting some fasteners and lumber from the Logging Camp:
You examine your supplies. You have:
X "appropriate" pieces of lumber
Y "appropriate" fasteners
First time only:
You use some of the horrible building materials from the smut orcs' camp to start building a bridge.
Subsequent times:
You use some more of those horrible building materials to continue constructing a bridge.
Upon completion of the bridge:
Huzzah! The bridge is finished!
And having finished the bridge, you throw away the rest of the smut orcs' terrible building materials. Good riddance.
After completion of the bridge:
Unless you want to blow up the bridge you just built, Alec Guinness style, there's nothing more to do here.
Notes
You have to collect a total of 30 "appropriate" pieces of lumber and 30 "appropriate" fasteners to complete the bridge, allowing access to The Highlands.
The Smut Orcs are probably foreshadowings of the XXX pr0n on the far side of the Chasm – their name is the word "scrotums" spelled backwards.
Alec Guinness is an English actor who starred in the movie The Bridge on the River Kwai, where he played Lt. Colonel Nicholson. In the movie, Nicholson and his fellow P.O.W.s build a bridge for the Japanese, then blow it up in the end.