The standing water sounds more like clay than sand. With sand, water goes right through past the 'root
zone' too fast to be of service to the grass. (this is my problem here). Clay is tough stuff to work with. The best results (for both clay and sand would be to till that manure and peat and any other organic material that you can get your hands on right into the top few inches of soil whenever possible. And cooler weather is best for starting grass
seed. For me in s. Cal that means fall through early
spring. Is is easiest to keep it more evenly moist then. So probably now is best to start.
I see southern Nevada as your
growing field. Anywhere near the Colorado River is a very hard place to plant. The area there is, beside being clay, almost too alkaline for most plants to thrive. This is the reason why the River has not ever had a lot of over-grown jungle growth and thickets in the sides of it. Most people in the area have dug out their yards by feet and then brought in huge truck loads of topsoil in order for grass to thrive. And have gone even even deeper for trees and shrubs and still have to add yearly applications of acidic material or food. And my aunt in Henderson planted most of her
flowers and vegetables in raised beds with imported soil for the same reasons.
I would ask at your local extension office or or university or something for the best ideas for you.