Will they be up there throughout Sept?. Yea, some at and above tree line but can be force down with a heavy snow storm. As frost kills the grasses up there, the elk will migrate down some to find better food. Also hunting pressure in early Sept. will cause them to seek refuge in the timber at a lower elevation. When the rut comes in strong, all bet are off as to where they might be, as they were earlier.
As the rut fires up, elk seem to start to concentrate lower (around 8500 where I hunt...tops are 10,500). I'm not sure how that applies to areas with generally lower elevations, this is just my experience where I hunt.
In which case it probably pays to figure out an ambush spot that puts the thermals in your favor.... though I never seemed to be quite high enough, early enough...
As Paul points out, elk follow the snowline up from their wintering grounds. In the areas I hunt, many, if not the majority of cows remain quite a bit lower than the bigger bulls. During the spring and summer months, the only elk I'll see are cows, calves, a few spikes, and even fewer young bulls. Around the 3rd-4th week of August, the satellites and wannabe herd bulls start showing up. They'll gather up a few cows/calves and think they're King of the Hill. Around the end of the 1st week of September, the big boys start showing up and take over the harems that the little guys were so kind to start rounding up for them.
No doubt, there are elk higher up than where I hunt, but I've made my living hunting elk in the 7500-8500' range.
One area I hunt, all of my hunting is above 10,000 and I killed a bull at 11,600.
Early 2000's: My experience in the San Juan NF I was into elk (bulls and cows) at 8500' near a water source. They had 12,000' mountains near by. The wallows I hunted were 1 1/4" miles from a main road on the east-northeast side of a 9400' peak. lots of blow downs and pretty thick with oak brush near the ridges. Elk seemed very fond of some benches just above the water where I killed a cow (muzzy) at 1:30 PM. Cover was broken here and the terrain was much more forgiving. My buddy took a cow with his bow the following year on trail descending from those same benches to the water source. They routinely came down to water from the bedding area on those side-hill benches. Two years later on a late afternoon hunt, the same friend killed a fine 330 bull not 50 yards from the location of his shot at the cow. The elk spent the majority of their time on the benches and near the water just below. The steepness, distance from the road, and the nasty cover all around this spot gave the elk some peace. We tried to have a low impact on them, and that seemed to work for the most part. This unit is OTC and gets hammered by hunters for bow and 2nd & 3rd rifle. It all when to crap when the ranch that rented us cabins was sold. With out the access from the private land, it limited the approach to the long-way-around and a potential uphill pack out. Did not fully understand how good we had it! LaGriz
They don't seem to care much about temperature either. I have a photo of a herd of 150 feeding out in the foothills sagebrush in mid-afternoon in July at 6000' when the truck thermometer read 93. The nearest tree was miles away.
Find the cows and hunt them, and the bulls will come. Bulls travel many miles to where the rut happens, and often return to the same place year after year.
Water, eats, bedding shelter and seclusion.
I have hunted elk in the sage and pj/cedars of Az. (3,000--6,000ft)to the High treeless/krumholz basins in Colo.(10,500--11,500)
Nice to know I should be looking lower... especially as I get a little older...