Hard to say but could be some sort of mildew disease. It's pretty common in cukes. They like their soil consistently moist, but not too wet, and if it either dries out or is soaking wet for too long they tend to sulk and get sickly. If you're in the hot parts of NV keeping consistent soil moisture can be a challenge. A layer of mulch might help. Also keep an eye out for cucumbers because if you leave them on the vine too long the plant will stall in production. And if you don't have a good pollinator population around you may want to try to hand pollinate and see if that increases your production.

There are a lot of discussions about cukes on the Vegetable Gardening forum, which is quite a bit more active than this one. Just make sure to mention your general location when you post a question because that can help a lot to narrow down the potential problems and get to a solution faster.