here. I played with it and found it to be quite useful, although the scale is too small for extremely detailed work.
The zoom feature in the upper left will bring you in to a scale close to about one inch equals one mile. If you hover your mouse over a particular color (rock formation), its symbol appears in another box in the upper right. If you double click on that box, the legend description appears in a larger box to the right. There is a tab there that takes you to its description in the legend. Here is the geologic map with detail at full zoom, centered on the House Mountain volcano just south of Sedona, Arizona.
It's fun to zoom around the state and see what is where. Enjoy and thanks to AzGS for this tool.