I will be visiting Colorado, and RMNP in particular around September 12th of this year. Also, any information on viewing big horn sheep in the park at this time of the year would be very helpful. I have visited in early September for the last 3 years and the elk will definitely be in rut. Their bugeling can keep you awake at night if you are camping in Moraine Park.
Some trails are a bit dicey in early morning and early evenings because the elk are roaming.
We were challenged by one bull elk who did not want us to pass, and one definitely does not want to bother a bulk elk in rut. Also, on Fall River Road before Lawn Lake TH there is a big horn sheeping crossing marked by signs forbidding cars to stop in order not frighten the sheep. Alas, hordes of people stopped and chased after them to get photos. We will be visiting RMNP from Sept. 21 to Sept. 25 and are looking for areas to view Elk without hordes of people around. Start out on the Deer Mountain Trail and take the left-hand trail at the top of the first hill.