Replying to Intense Hikes

so has anyone ever done a 25 mile hike through a pretty thick forrest w/ no trail? me and like 5 other friends are planning on hiking from reno to lake tahoe, and there's no trail from where we're starting, actually there is but it ends after a mile and a half then your on your own for the rest....anyone have and experiences w/ hikes like these or any advice...one of my  friend is an eagle scout and a 2nd degree black belt, just thought id throw that out there