Apodanthera undulata (Melon Loco) has been added to my Wildflowers of Tucson, Arizona website. It is currently blooming here in Arizona.
These sprawling, yellow-flowered vines with rounded leaves are often found growing along roadsides, and are especially common in areas south of Tucson. These native plants do produce melons, but unlike those of some other members of the Cucumber Family (Cucurbitaceae), Melon Loco fruits are definitely not edible. Generally, it's best to avoid eating any plant with loco (Spanish for insane) as part of its common name, as this can mean that the plant is poisonous with behavior or mind-altering properties. I don't know if Melon Loco is actually poisonous or not, but you would probably have to be crazy to eat it because it has a horrible, bitter taste.