Starting from the Park & Ride at the "Y", intersection of Highways 2 & 97 near Peshastin (elev 1000'), go south on 97 (Blewett Pass Highway).   After about 3 miles, turn right on Campbell Rd., which parallels the Highway for about 2 miles.  Back on 97, continue south for about 2 more miles and turn left onto Old Blewett Pass Rd, paralleling the Highway for about 1.5 miles, turning left back onto the Highway at that point. 
     At your mile 13 (about 1/2 mile past mile post 173), bear to the right onto Old Blewett Pass Road (elev. 2400').   From here on, about the only "traffic" you'll encounter will be other bicycles.   In about a mile, the pavement crosses Scotty Creek, the road narrows, and the grade increases to 5%.   The climb is basically a series of curves along the side of the mountain for another 5+ miles to the 4071' summit.
   The pavement here can be somewhat suspect, with occasional gravel or sand patches, and sometimes small rocks on the road.  But potholes had generally been patched and, all in all, the road was not in bad shape on my last climb (May '06).   In fact, I was able to keep up a steady 30 mph with little worry on the return descent.
    From the summit, the road continues to curve downward, another 4 miles until it finally intersects with the modern Highway 97 (your mile 23, elev about 3100').   The surface of the south face is typically in much better condition than the north -- with few steep road cuts, there tends to be much less debris on this section.   On my May '06 climb, the pavement of this south slope was quite clean.
     From the intersection, riders can opt to climb over the "new" Blewett Pass (elev 4102), making this into a loop tour, but having to deal with the trucks and other high speed traffic.   My preference is to simply turn around and back-track, taking in the climb and descent 180 degreees from the outward leg. 

      Although about 8 miles of Highway riding in each direction is required near the start and finish of the ride, shoulders are generally wide and traffic isn't nearly as heavy as it is on Highway 2.   And there's the distraction of Peshastin Creek alongside on the upward leg, and the exhiliration of the slight downhill on the return -- although it's not uncommon to have a headwind over the final few miles of the ride.

     But the highlight is definitely the Old Blewett Pass Highway -- kind of like mountain biking on your road bike, on pavement, on a "bike path through the forest".