The total elevation difference for Clark Trail is 1,415 feet which is an average number. Being 7.2 miles long it's a mid length walk. This is a one trailhead trail, so in and out is the way to trek it normally. You spend the whole walk in roughly the same elevation zone which means the conditions are about the same from start to finish. This backcountry walk shouldn't take more than 6.5 hours, but of course some people walk a bit slower and some a bit faster. This is a trail that is quite long, so do pack enough food to last the whole trip. At parts of the year this area sees very little rain, so make sure you check current conditions and fire restrictions with local forest authorities before you head out.