I do most of my walking on "unconventional" surfaces, too.  I'm an avid backpacker and hiker, and I don't think any of the cc activities really take into account all of the variables that come along with walking in the woods.  My solution is to use a heart rate monitor that gives me a reading of calories burned.  I can add it in manually to my activity log.  Walking on sand would definitely add some effort, and the hills and uneven surface make a big difference.  If you can't buy a heart rate monitor, I'd use  a faster speed than you're really walking to make up for the extra effort.

While I have nothing of any value to contribute, I would just like to say I am most envious of your walking environment. I see a lot of snow, a lot of rain, a lot of traffic, but sadly no sand. Your are truly fortunate!!

Thanks for all the input. If there is ANY mud in the desert, I will be the one to find it.  My dog and I did find some just yesterday.  I decided to change up the route some, and veered off through the desert in another direction.  We came upon some pepper fields and had to find a way around the aqueducts.  This meant we had to cut across the corner of a field.  Murphy seemed to enjoy being  up to his belly in mud, however, I wasn't too fond of it...........the only choices were to let it dry on my shoes and feet or to dunk my shoes in the water and walk home wet.  It was a whole new experience in walking with ankle weights!