Best bet for close-in riding right now is the Ridgeline Trail in south Eugene. It’s got a lot of gravel but it’s in the woods and you can get a great workout. I do variations of it from my house near the UO and typically get 13 miles and 2,000 feet elevation gain.
Ride up the Headwaters Trail from Martin Street to Fox Hollow then over to Dillard Road and up and over Mt. Baldy to Spring Blvd. Turn around and climb back up and return. You can do laps on the climbs for more elevation gain if you want.
Note that there are alternate trails on the Fox Hollow and Baldy sections that are closed to bikes. And if you need any more info or directions go talk to the guys at Life Cycle Bikes—Ridgeline is their go-to after work ride.
MTB trails at Thurston are closed due to wet, clay soils. We tuned and rebuilt a lot of the berms over the last few months and it would be good to let them set up, dry out, and harden. Heard that Willamalane plans to open the trails in June. Trailwork at Thurston on May 18, come on out!