The Spitzer Space Telescope's infrared senosrs detected the ring starting about 3.7 million miles from the planet to about 7.4 million miles, overlaying the orbits of the moons Iapetus and Phoebe. JPL researchers think Phoebe is responsible for the material in the ring, and that it could explain the dark face of Iapetus, which orbits through the ring and counter to it.
http://news.yahoo.com/s/ap/20091007/ap_on_sc/us_saturn_giant_ring