Hillmap now lets you create slope overlays for arbitrary slope angles fo most of the united states. To try it first zoom to your area of intest and then, click on the "Hillmap Slope Analysis" tool on the "Data and Analysis" tab.
The default values work well for identifying slopes steeper then 30 degrees which is useful in planing trips to avoid avalanche terrain. You may find that other values work better for identifying steeper or lower angle slopes.
Once you have created a slope overlay you can zoom and pan to explore it using the standard Google Maps interface.
This tool uses modern web technologies so you will need a modern browser such as Chrome, Firefox or the Internet Explorer 9 or higher.