Bob!
Congratulations on your Intermountain windfall! Like friends with pools and boats, we all need friends like that!
One thing as long as we're on the topic and especially for folks new to using flex, here's what I was told and it works, for me at least.....
Buy a rail cutter (nipper) at your hobby shop. It looks like a regular wire cutter. DO NOT USE IT for cutting wire or anything else. Remember your mother giving you hell if you tried to use her sewing shears for anything other than material? Same concept. don't forget a small, fine metal file while you're at the store.
When cutting rail, cut ONLY with the flat side facing the side you wish to use. The other side will give you a convex cut which must be filed flat, which is a royal headache if you've forgotten what you're doing, as it's time consuming to get it right. A nice flat cut requires minimal filing
When you lay a piece from a straight section into a curve and run out of the length, lo and behold, one side will have more rail protruding than the other. DON'T PANIC! Most people mark both rails with a small file, then cut the rail at a parallel point in the curve. I do not do this.....
Take an Exacto blade and cut the single tie off the track frame nearest the short end. Next, take the blade and razor off the tie plate grips that hold the rail. Put that little tie aside.
Remember I said to keep the sliding rail on the OUTSIDE of the curve? Great! Take the next piece to be laid, and work the sliding tie into the protruding ties on the short end through the tieplate holders (plastic "spikes") to the short rail. Remember, where they join, you have to cut usually 2 ties away to fit a rail joiner. Put it on and crimp the sides down to hold the rail firmly. Now get the other side together the same way by cutting wherever necessary.
The result is that you have succeeded in staggering the rail joints. This will hold together better for a smoother transition for your cars from one piece to another, especially on curves. The problem with making a parallel cut on a curve is that it's difficult to get the track leading into the next piece without a kink at the joint.
Now you have some unsightly gaps where the railjoiners are located in the run. Take those spare ties you razored the plastic spikes off of, and SLIDE them underneath the joint with appropriate spacing. You have now done a pretty sharp job on concealing a rail joint of Flex Track.
On straight sections, don't forget to leave a slight gap at every two joints for expansion, depending on your local climate swings.
I hope this makes sense. Give it a shot and you'll figure out the concept quickly enough.
One last thought. I've said it before here @TG more than once, and I'll say it here again. Don't chince on buying Flex. You can save some pennies buying Model Power Flex over Atlas, and it just isn't worth the aggravation if you're not used to working with Flex. Atlas holds up better while you are working with it, and it has superior detailing on the ties. Stick with Atlas.
Happy Rails To Youuuuuuu!
George.