how is the canyon floor a different World than the country surrounding Davis gulch

From the text:

"The country surrounding Davis Gulch is a desiccated expanse of bald rock and brick-red sand. Vegetation is lean. Shade from the withering sun is virtually nonexistent. To descend into the confines of the canyon, however, is to arrive in another world. Cottonwoods lean gracefully over drifts of flowering prickly pear. Tall grasses sway in the breeze. The ephemeral bloom of a sego lily peeks from the toe of a ninety-foot stone arch, and canyon wrens call back and forth in plaintive tones from a thatch of scrub oak. High above the creek a spring seeps from the cliff face, irrigating a growth of moss and maidenhair fern that hangs from the rock in lush green mats."