We enjoyed driving to the very top of Brian Head Peak, NE of Cedar City in Southern Utah. We visited in mid-September and oak at lower elevations were showing spectacular reds and the higher-elevation aspen were just starting to turn.
Just under the peak we found large, highly-colored agate scattered along a small stream bed and all over the adjacent hillside. This was some of the best agate I've ever found. You could gather up small pieced by the bucket full. If you use tools you can pry out some large pieces – as big as you can carry.
The drive is worth it just for the scenery. If you enjoy rock hounding, this is a great place. The agate is easy to find and so this is a fun area to bring kids.
Latitude: 37.674168°
Longitude: -112.833986°