I'm guessing shorts will fix it, too. The main reason to wear them isn't for the padding, which is too thin to do much good in most cases, but to eliminate chafing. If you don't want to wear Lyrca (I don't), then mountain bike shorts work fine, or get some cycling underwear, which fit like Lycra bike shorts but can be worn under regular shorts. REI carries them for sure. One brand name is Andiamo.
Jeans are death on long rides. i started mountain biking in the early '80s, when it was pretty much mandatory to wear jeans and a flannel shirt. wore my thighs OUT...