I used the Gaia app on my iPhone last year when I rode from St. George, UT to the Bar 10 Ranch. It worked great, especially for $20. Note: this app will work even when out of cell phone tower range using the satellite receivers in your smart phone. I will say there is a bit of a learning curve and I brought paper maps I printed at home and hand drawn maps I made myself as back ups. Never had to use those though. Just stopped every once in a while and did a spot check with Gaia to make sure I was still on track.
Gaia GPS helps you find your way anywhere, even offline | Macworld