Summary - There are two routes up from Zigzag Mountain Road (Road 27 from HWY 26). The longer route follows the West Zigzag and Zigzag Mountain trail and ends in a bushwhack up the northwest ridge of Zigzag Mountain (about 5.5mi OW). The shorter route follows Burnt Lake trail to Devils Tie to Zigzag Mountain trail and ends in a bushwhack up the north side of the summit. (about 3.5mi OW). I recommend the longer route, which meanders along the mountain ridge, and is less used. ATT digital service was spotty, APRS was full strength, 2M contacts aren't difficult. HF setup is easy.
TL;DR - This was my second visit to Zigzag. The first time, I hiked the shorter Burnt Lake trail, an seven mile out and back route with 1800 feet of up. This round, I made a loop of it, taking the West Zigzag trail up and the Devil's Tie and Burnt Lake trail back. This is a roughly 11 mile route, which climbs 2400 feet and traverses all four high points of the Zig Zag Mountain ridge. I highly recommend the loop hike as the trail up is much less traveled and the views along the traverse are fabulous.
Zigzag Mountain Road (aka Road 27 off HWY 26) is rough and potholed but passable for careful passenger car pilots, at least when it is dry. I did encounter both a mud pit and a pond that required extra care, so YMMV. The loop trail begins at the 789 (West Zigzag) trailhead, which is about one hundred yards below the parking area and the Burnt Lake trailhead at the end of Zigzag Mountain Road. The trail climbs about 800 feet in the first three-quarters of a mile, drops and then climbs another 800 feet in the next mile before reaching the first high point on the ridge, so it is a pretty stiff start. The next three miles of the hike is more gradual as it goes along the ridge and brings you to the bushwhack.
For the bushwhack, I decided to go up the nose of the northwest ridge (45° 20.8544' N, 121° 50.3586' W). Coming from the other direction, most people opt to slug their way up the northeastish slope. The northwest approach isn't quite as steep but there's a lot of tree fall while the northeast approach is thick with brush. Pick yer poison, I guess. The summit is small, flat, and covered with bear grass. There are trees for hanging wires but not much shade. ATT cell service was pretty spotty but APRS works well. Most people hiking this trail are heading for one of the lower high points on the ridge (which have beeter views). Combine that with the bushwhack to the summit and you are unlikely to have company.
Hike back by picking up the trail on the north side, below the summit. Turn west to go back the way you came, east to take Devils Tie and Burnt Lake back to your starting point. Two notes: First, the trail is easy to follow either way but a map and compass or GPS will be handy for tracking the turnoffs. Second: the parking area holds roughly ten vehicles and the trailhead is popular on weekends; an earlier start is advised.