I'll pitch in here: I hunt pretty much only dark timber these days in CO it seems like. I'll also second Mallards post above: you think you know thick, nasty, and steep but... ive broken more hunting partners on day 1 then i'd like to admit in these locations: There are elk, there are multiple bulls, and with Gods good grace they'll be in there again next year.
When i scout areas like this im looking for elk highways through the thick n nasty: i mean it looks like elk are coming through and crossing off pretty regularly and created a muddy path a meter wide. Naturally there are elk tracks, poo, whatever on this trail and none of those matter so long as i can see its a place elk are moving through.
I look for wallows: If theyre used? Fantastic, if theyre not this year? Well at least they were at some point.
I look for rubs from multiple years: I wanna see ancient rubs, 3 year old rubs, 1 year old rubs, rubs from this year, all of it. This tells me they are here pretty regularly during the rut, and, as mentioned above, if Gods smiling down on me, they'll be in there again this year.
Listen: while your way off the road: bugles dont travel far in that thick stuff, but you can hear em still.
Dont move fast, your basically surrounded by bedding area, its ALL potential bedding area. I find elk beds just allll over.... which is what it is... they bed in thick timber.
Respect that knowledge: its a bedding area, if you royally ef this over they arent going to feel secure in this area and will beat feet out of the unit for a long time. soooooo:
Pay attention to the wind, dont make a move on where you think there are elk if the wind is swirling.
Seems like "Dark timber" has a lot of definitions these days, and where i find the most success is kind of a changing habitat with beetle kill and deadfall. Here's the thing: it WAS deep timber... now its just habitat. It has enough sun that there is food underneath the canopy, there is water in abundance, its nice and cool, and there is cover. They dont need to move a lot in these habitats to find what they need in my experience and i end up hunting the same bulls day after day... and yup, they dont always move very far either. I have a spot that i walk up to in the morning and almost every single time am greeted by a bugle just from breaking twigs moving through the steep n nasty. I've never seen that bull. Ever. Multiple years in a row. Just too thick and he wont come down to calling for me.
I'll add an edit tip here too: I like to give a few quiet cow calls if i feel like im making a lot of noise while im moving: sometimes you just cant be quiet in these thick areas and i'd rather pretend im a 2-legged, bad at moving in the woods cow elk then the truth: im a 2-legged, bad at moving in the woods human.