Peas suffer in the heat?

Hello all, I have 2 squares of bush peas in my elevated bed(36" off ground). They turned yellow in one day. I was gone on a MC trip all day Saturday which was hot 90+. My wife watered twice about a cup each square, seems like enough. The elevated is MM soil.
The odd thing is the in ground raised bed square of peas in a soil/compost mix look great. 

So I'm thinking what is the difference?
 1. The in ground is 50% compost while elevated is 33%. So maybe needs fertilizer?
 2. In ground plants have tap deeper water source while elevated are basically container plants strictly limited water? Also would the soil/compost hold more water? 
I'm so new to this that it is all NEW to me  
OC

It could be something such as soil temperature. Remember, peas are cool weather crops. If you have a soil thermometer, test the soil temp both for the above ground and on-the-ground bed. Plants keep cool by pulling cool water from the soil, and up into the leaves where the plant perspires to cool off.  if the soil is hot, the plant cannot pull up cool water to use to cool off.

Another problem with the above ground bed might be an inability to drain excess water. Peas will develop yellow leaves from too much, or too little water. They don't like their roots to be saturated in water. If the bottom of the bed is saturated with water because it cannot drain out, that will cause the leaves to turn yellow due to too much water.  Check deep in the soil to see if it is too wet.

Hi OG, 
I did not remember peas are cool wether
Thinking about soil temp. 90+ air under, direct sun on the sides. I suppose for all the neatness of elevated it's just a big container and suffers the same drawbacks. I do have a remote thermometer I can put a few inches down. My engineer brain demands I know the answer to that "how much heat" problem.

I suppose on these oppressive(for me and the plants) days I need to rig a shade for the container. 
Now the burning, Pun intended ,question is "are these peas toast?" can they recover or what??

As for draining I think it "should" be OK. the bottom is hardware cloth(1/4 wire grid) with a sheet of landscape fabric over that. I thought that landscape was not water proof. 

Thank you very much for those thoughts/insights. 
OC

Peas can be planted as soon as soil can be worked, OC.  Here, usually around St. Patrick’s Day.  Also they are nitrogen fixers, if your MM is fresh I doubt it is due to a lack of nitrogen/fertilizer.  My sugar snaps can generally weather a short stint of warmth, but they don’t like heat of summer.

Live and Learn. Turns out I've mixed cold and warm in the elevated box, mostly cold with only cucumber, bean and dill warm. 
I went through a book by "The Vegetable Gardener's Bible" by Edward C. Smith and looked at all the max soil temps for my vegetables. As you would expect the cold stuff is mostly about 65F while the warm is 75-80F with my peppers in 2gal bucket being the king of hot at 85F soil temp max. 

Edward doesn't specify depth so I measured 4-6inches down in shaded spots.  

Now the crazy part I measured the soil temp about 4inches down in my pepper Homer 2gal bucket with a mylar reflective skirt and partial sun on my sunroom porch and drum roll please... 95F. 
Next I measured the soil temp in my in ground MM bed and it's 80F while the shaded container is 82F(which is the outside air temp).

So I had a bunch of mylar emergency blankets from another project, I've cut one up for skirts for all 7 of my buckets. Next I had an unused broken patio umbrella so today on a much milder day but still above our normal summer time high, this is my elevated container.  Easy Peasy

Nice!!!!  Looks like a good stop gap,   OC.