>>1218947July and August growing season?
https://laramiegardenclub.org/gardening-at-7200/vegetables-fruits/I highly recommend polytunnels with 1-2 layers of plastic and/or greenhouses with polytunnels inside. There are several cold hardy cultivars you can get online. Some have really short seasons so you'd only need to cover them well at the beginning and ending of the season. I'm not sure it would work, but Painted Mountain corn (a flint corn) is 85-days to maturity and bred for short seasons in mountain areas. Though, I'm not sure it gets up to 7,200 feet. It'd be worth a try with cover. You can even grow them in pots and they grow rather short in height. The only concern is light. corn is triggered to flower and fruit when days get shorter. So, you may end up with really short stalks and smaller ears if it is triggered sooner than normal, but only if the daylight is being restricted; like if you live in a deep valley.
Onions you'll need to plant from sets. Cucumbers, chilies, & tomatoes should be started indoors with plenty of light using short season crops, hardy for cold. I have some of the shortest season peppers in my garden, but I'd like more (Hungarian Wax Pepper [hot] and Gypsy Red Bell Pepper [sweet].)
Cucumbers usually have really short life spans anyway for the most part:
https://www.gracegardenandhomestead.com/how-to-grow-cucumbers-the-warm-weather-crop/Tomatoes:
Orange Pixie
Siletz
Alaskan Fancy
Aurora
Beaverlodge Slicer
Oregon Spring
https://northernhomestead.com/growing-tomatoes-in-cold-climate/If you decide to try planting in pots, I recommend getting a large-wheel dolly aka "hand truck" (pic is specifically for moving pots) to move the pots around. That will be easier on you and the containers when they are full of soil. Large diameter wheels are much easier to pull (don't push) across rough ground and bumps. Also, get ones with solid tires, not air-filled ones unless you like extra work over the years airing them up before every use.
