This is a Red Racer (Masticophis flagellum piceus)-
a diurnal and very fast snake of Red Rocks, Nevada.
Photographed in Fern Canyon in spring 2007.

Notice the presence of black marks on head and neck and the lack of marks on the rest of its thin body. This snake is often described as a red snake with a black head.
It will bite, excrete musk and twist its body when handled.