I agree with everyone else...you two should do what you want to do. If you're family is making a big deal out of it and you want to, maybe let them help you plan another ceremony or reception for when you get back so that they can celebrate with you. Personally, I'd go with the reception thing.
It sounds like this Tahoe thing is really special to you and Jeff so I think you should go with your plans.
I don't know anything about Tahoe, but maybe ya'll could wait until the end of the trip and then stay somewhere really nice where you could get married. Or if the route you're taking for mtb is accessible via car or ATV maybe you could arrange for a photographer and minister (or whoever you're using) to come out to you. Just some suggestions.
Gray