There are actually three ghost towns on this loop, but only two have any real ruins left. Sasco (Southern Arizona Smelting Company) is the first town coming in from Red Rock (mostly graded dirt; exit 226 off I-10). It was built in 1907 and served as the smelter town for Silverbell and Picacho Peak mining. The most visible set of ruins are in Sasco, particularly the walls of the Rockland Hotel (N:32 32.182, W:111 25.906) and the smelter ruins themselves (N:32 31.997, W:111 26.328).
The original Silverbell (one word) was located between two towns, with 3,000 residents from the 1860s to the 1920s. The town included a post office (1904) and a Wells Fargo station (1906). A shaft fire in 1911 and falling copper prices forced the closure of the mine in 1921. A reminder of the many people and hard life that was here can be found near the cache site (.6 mi), including the name of this cache. No other ruins remain here of the this town.
The newer town of Silver Bell is located at the point where the road begins heading east towards Rillito and becomes Avra Valley Rd (mostly paved; exit 242 off I-10). This town was populated from 1948 until as recently as the 1980s when the copper mine was again in production. A few signs remain, although most buildings were sold off and moved.
One final note: much of this road is former right-of-way for the Arizona Southern Railroad, particularly the 13 mile stretch between Sasco and Silverbell. It was built in 1904 to shuttle ore from the mine to Sasco for smelting. The rails were taken up in 1934, but the nice wide low grade road remains in its place. In fact, there are a few very unusual spots where you'll note this remote desert road cutting through instead of over some low lying hills, revealing its railroad past to observant cachers.
Enjoy the drive and Arizona History!