If it were me, I would just take Manastash Rd back into Ellensburg, and take either I-82 or the Canyon Road down to Yakima, then up Hwy 12 through Naches and on to whatever part of the Bumping Unit you're headed to, I guess either up towards White Pass or farther on up towards Chinook Pass and to Bumping Lake area. It's quite a long drive for only being around 20 miles as a crow flies! It will be at least 1 1/2 hours.