I would be more concerned with snow than cold that time of the year. It can be a very wet and heavy snow also which is no fun at all. You can very easily get stuck for days with a big storm and the weight of the snow on the tents can crush them. You said car camping which is a concern unless you are on some very easy access road. A truck is allot better option if it is possible. Putting a trap over your tent will help a little but it can easily come crashing down or rip too. I would check the weather as often as possible as storms have a way of popping up. Last, you might not even be able to get where you want if the snow has already started to fly so have a plan “B” just in case. Of course as Still Hunter said, could be 80 degrees but not usually.
If you have lived in Colorado longer than a year you should know that in October you can expect any type of weather that there is. It may be hot and dry but then again you may have 5' of snow and below zero temperatures. But then at 11,000' elevation you can expect for it to be cold at night and cool during the day. You just have to be prepared for anything and everything.
As I have always said, "prepare for the worst and hope for the best"
Yeah, I have a 4x4 truck not a car I will be camping from. I will keep track of the weather leading up to the hunt. A hotel 30 miles down the road may be my plan be and another area with lower elevation and easier access will be my backup plan.
Get yourself a set of chains for your truck and I mean chain chains not the cable type, and learn how to put them on while it is nice and dry. 1 set will work but 2 are better. Also get some 36" bungee tie downs to use to tighten up the chains.
I have seen where traveling even 100' stopped a truck until the chains were put on.
I wqas camped at 9800' last year while elk hunting in mid october. We went from 60-70 degree days to 1.5' of snow at camp. I ventured up a bit higher a few day after the snow finally stopped and at 10500' there was about 3' of snow. the snow we recevied indeed was a very wet snow and with in a few day lot of it had just melted into the groud it was not real warm to make it muddy just enough to drop the depth of it down. We hunt from a Alaknak wall tent(a real think nylon sort of material), the snow really sagged down the top and such and it did cause alot of mositure to start to seep inside the tent as the snow was not on the tent much just so much water coming down in fromk the tree....things are only water proof for so long. I think if you can get a tarp over your tent it will help a bunch. I would sure take along a real 0 or lower degree sleeping bag even at 60 degrees in the day it gets pretty cold at night that high up. We have a stove so the tent stays pretty toasty.
Not sure why you'd want to camp at 11000' in the Rockies in mid October? You could camp a couple thousand feet lower and just drive up to where you want to start hunting. You would likely be more comfortable. Any special reason you'd want to camp up that high that time of year?
The record books, that are put out by Boone & Crocket and Pope & Young and where I live is Henry Kelsey they are a great way to research a state or a province for big game. This does take some time but the knowledge it gives you, can be very valuable. Not all hunters have their trophies recorded, as where I live after the Hanson Buck became the new world record typical Whitetail, we saw a flood of hunters and now that has happened, some hunters are shying away from the record books but...