Marathon long run question

My concern would be an injury during your 20 mile day.

I know that I would race the 10 miles hard, then stand around for an hour eating post-race food. The second 10 miles would be on cramped up/exhausted legs.

Since the point of those long runs is just easy miles, do the second set super slow. If you feel any tweaks, just stop for the day.

It may be a little risky, but I would do it myself with full confidence. Good luck on both races!

Well, maybe just take one thing at a time. See how the 18-miler goes this weekend. I'm not sure what you have done leading up to the 18. I am assuming you haven't gone this distance and the 14 miler planned for the 6th was a purposeful step back. 

Also, the point of doing those 20-milers is to train for endurance. Racing a (I assume) fast 10-miler, taking a break and then doing another 10 isn't really giving you the same training stress. 

Because you are racing just to finish, I think I would be more conservative with whatever you choose to do. You already know you are going to finish, you would hate to set yourself back from that goal.

Additionally, in terms of elevation gain and loss. All I can say is that you should be training on hills (up and down) throughout your plan.

So last week was a step back 12 per the plan and felt surprisingly fantastic.  Week prior was 16 that did not go well, not due to anything other than heat - I ran it in the afternoon when I've been doing most of my runs either early or evening.  I have no doubt that I would have been able to do it just fine had I not started at 1pm (in AZ).  

Nothing is fast for me - my plan is a 5min run/1min walk and I've done that from day 1 with a few exceptions (I started not walking during the 3 mile runs that were in the plan a few months ago).  The upcoming 10 mile run is a trail race that will most certainly be slow due to the 92 or so stairs in the middle (twice).  I've been trying to do all my longer runs on trails because it a. slows me down and b. is a better prep for the marathon which is all forest road c. is a little more scenic.

The point of including the basic elevation was that I'm pretty confident that I can at least roll downhill, worst case   So I really need to get back up to mile 17ish and then so long as my legs don't cramp into angry balls, I can probably trot back into town.  Pretty sure I won't be leaving town under my own power, but I should hopefully make it there.

I'll see how tomorrow goes and then figure out what to do next week.  

Don't worry about it.  If your goal is just to finish, then don't sweat the details of one run because it's not going to make that much of a difference anyway.

People get WAY too caught up with the long run distance when it's more about the overall volume and consistancy you have run over the course of the past 4 months, year, or even 5 years.

If you're really worried about making up the distance in your plan, then just add some miles to your mid week run to make up for a shorter long run.  Miles are miles.  It's not like long run miles are magically worth 2-3x more than any other miles you run during the week.