Hello Steven, 

Are you using above-ground irrigation in your backyard? This is very common for ponderosa pine that are in direct contact with water from sprinkler systems, as the water causes the tannins (brown/orange coloration) to leach from the bark, leaving them bleached. This is not caused by disease and the bleaching will not cause any harm to the tree.

If this is caused by a sprinkler system, you can try to reduce the flow or aim the sprinklers lower to reduce the bleaching and they will eventually become brown again as the outermost bark peels off. Given that we are in an unprecedented drought, you can wean the tree off of irrigation slowly if you are looking to reduce water use in your yard.

I hope this helps, 

Thomas