what has the weather been like in Arvada since Jessica was abducted? any rain or snow? If the tire tracks were fresh it could be a good indication of when Jessicas remains were left there.
I think they said it was snowing or was on the verge of snow when Jessica was abducted. Someone posted a few pages back that it was raining (at the time of posting, not at the time of abduction), and commenting that rain was rare in Colorado.
Footwarrior will likely know, being a local.