On Saturday the Forest Service told us about an app called Avenza. I tried it and it is great. Load the app and then you load the map. There are a lot of maps available now, mostly Forest Service maps. In the future I'm sure that there will be many more. Now the maps that are there are the exact map that you can get on paper from the FS office. The map can be moved and zoomed to see all of the map you need. If you have your GPS enabled the map will move under the I am here icon. It works with the map loaded on your phone so you do not have to be connected to cell service. Best part is it's free and there are about 20 NF maps for Colorado.
I have used an app simply called Topo Maps for years. Download the USGS topo for an area and the internal GPS puts a blue dot on your location. You can also save waypoints and it has various other cool features.