Oops!
Sorry Disneyson I never got your comment (I posted mine before yours' I guess) so I will respond to it now.
First of all thanks for the nice comments!
Second thank you for suggesting to put the Thunderbird's lair at the exit of Big Thunder. I was considering that but thought that maybe it'd be better if guests saw it right away. But now that you mention it will be a much better idea to move it over to the exit. That way it will garner up more attention than it would near the entrance of the attraction. As a matter of fact there will be two options for guests after disembarking from their train. One path will lead to the left towards the queue and the rafts, and one path would lead into the Thunderbird's cave. The entrance (Which is very similar to Injun Joe's Cave in Disneyland) will lead into the walkthrough that I presented earlier.
Having the trains stop in the bird's lair might take away from the atmosphere just a little bit. The cave is a very quaint atmosphere (With the smell of chlorine! :lol
and a deep groaning sound that you can hear in a deep dark hole in the earth. I can't really describe what the noise is it's just a really cool kind of sound. Also the whistling of the trains might take away something from it just a wee bit. This was an excellent idea that you gave me though!
Since the Thunderbird is the primary cause of Frontierland's problems I will definitely use the idea of the Thunderbird's screeching being the cause of the earthquakes within the mountain. Also the catacombs where it resides will grow extremely chilly as you progress deeper and deeper into the earth. In the rooms that don't have water (I have decided to add a room shortly after the nest and before the General Store basement that is filled with a maze of waterfalls, similar to that garden-area outside of the Disneyland Hotel) the walkthrough attraction will smell like earthy-dirt. Not to the point of completely stinking up the place though.
At night the Thunderbird's screeching can be heard coming from the mountain (Similar to the roar of the Abominable Snowman on the Matterhorn) every now and then (Not repeatedly) while cave paintings of the Thunderbird legend (The one with the golden eggs, foolish boy, giant nest, mountain, peak, Thunderbird, thunderstorm, fledglings, earthquake, and buffalo) will briefly be seen in a tunnel quickly traversed by the Big Thunder Mountain Mining Trains. Hopefully this will make guests want to come back and get a second look at whatever the heck it was. This will also be the darkest tunnel in the entire attraction and the room where the "earthquake" takes place. This ride will use some of Disney's roller coasters best qualities, including the launch system of California Screamin', the speed and drops of Expedition Everest (And legendary monster theme/basis), the same setting and vehicles of Big Thunder Mountain, and the excitement of Space Mountain.
Again sorry for skipping over your comment!