When the mercury soars in the Sonoran Desert in the summer, the trails can be almost empty. The winter crowds are gone; snowbirds have decamped for cooler climates, and natives often wait for fall to start hiking again. For many who do continue, summer hiking is for early mornings, before the temperatures start their daily climb. But it doesn't have to be strictly an early-to-rise exercise, as long as you heed a few warnings. Temperature/exposure: Mornings are clearly the pri