From Evergreen Trail Guide
FYI: WTA will be there late December and Early January
Grand Ridge is both an oldie and a new trail: while new residential development wiped out some of the trails we rode in the past, a new trail system has been under development by King County Parks and the WTA. (Check out wta.org for work parties.) You access it the same way as ever: by climbing up from I-90. The trail can also be accessed from the top of the Issaquah Highlands development.
The main trail winds north across Grand Ridge towards Duthie Hill Park.
This is a great XC work out, with great climbing practice. Plus, it can be linked with trails on the south side of I-90 to create longer loops. This trail connects with Duthie Hill Bike Park and will eventually (10 years?) continue up to Soaring Eagle (aka, The Beav) for a suburban epic.
The climb from I-90 up to the plateau is a grunt, but not too long. When coming from Duthie Hill, the long climb up to Grand Ridge Drive is even more of a grunt, and is pretty darn hard to clean on a single speed. With gears, it's not too bad.
How to find it
Trail starts at KC Parks sign on RR grade on the north side of I 90 between Exit 18 and 20.
The obvious place to park is at High Point (I-90 Exit 20), on the north side of I-90. There are signs posted there warning of car break-ins, and there's little traffic coming by. Easy alternate is to park on the south side of I-90 where people hiking Tiger Mountain park. That area has also had car prowls, but will have much more traffic.
Another good starting spot is just off the Sunset interchange on I-90 (Exit 18), just as you drive down into downtown Issaquah. The parking lot is just to either side at the bottom of the ramp on East Sunset Way. From the parking lot head north over I-90 to the RR grade that heads east along the north side of I-90. After a mile or so you reach the Grand Ridge trail that heads up the hill to the left. (This parking lot is a good access to the High School Trail, described below).
A new paved trail - the High Point Connector - connects the East Lake Sammamish Trail (which turns into the Rainier Trail in downtown Issaquah) to the RR trail on I-90 east of Issaquah. This trail follows follows I-90 along the north side of the freeway. Folks living in Issaquah and Sammamish can use this link to get to Grand Ridge trails. (Note: Mountains to Sound Greenway Trust is working on establishing a bike link from these trails west to Eastgate).
There is also access to the Grand Ridge trail from the top of Issaquah Highlands. Go up to Harrison Way and then Grand Ridge Drive until you intersect with the Grand Ridge trail. DO NOT park on Grand Ridge Drive.
Yet another trail head is at Central Park in the Highlands (bathrooms). If you park by the tennis courts ride south the retention pond and find the trail at the south end or ride down the road under the power lines at the last tower find the trail that goes downhill on your right. They are working on a new trail that will start from the soccer fields, should be open early 2010.
Access from the north end. THE COUNTY ISN'T DOWN WITH PARKING ON ISSAQUAH FALL CITY ROAD! IT'S DANGEROUS! If you start early or on weekdays you can find parking at the Duthie Hill parking lot on Duthie Hill Road and ride south over the board walk up the trail through the clearing and out the access road. The lot fills up fast on weekends so it's best to park at the school at the corner of Issaquah Fall City Road and Duthie Hill Road or at the QFC lot at the light west of the school KC parks is working on more parking for the bike park. During the winter the bog at this end can have lots of water so be ready for wet feet. The trail starts just east of the gated access road. DO NOT PARK IN THE DUTHIE HILL CLEARING.
By bus from Seattle, Mercer Island or Bellevue (Eastgate), Sound Transit #554 or U-District or downtown Bellevue, Metro #271, or from Northgate/Bellevue during commute, Sound Transit #555 or from Seattle during commute times Metro #214 ( to DT iss and P&R) or #218 (to highlands P&R). For bus riders, from the corner of Sunset and Front Street in Issaquah go east on Sunset up the hill and across I-90 on the bike path.
Grand Ridge can have a few puddles during and immediately after a rain. Lots of leaves in the fall cam make for a really wet ride. Not crowded but does get a few hikers, families with small kids and dog walkers.
King County has completed the bridge over the first swamp. Rumor has it that they have plans to bridge/boardwalk the longer swamp that is at the north end of the trail.
12-6-09 bit of mud, bike doesn't need cleaning. BRIDGES ARE WET AND SLICK!
New map is now posted at trail heads. http://your.kingcounty.gov/dnrp/library/parks-and-recreation/documents/trails/bc_trails/grand_ridge_trails.pdf
You can also view a high-resolution GPS trail map for Grand Ridge from Switchbacks.com.
From the railtrail along I-90, head uphill at the trailhead sign. Within a short climb up (0.10 mile), ignore the left turn as the trail Y's. This steep spur trail leads up to Central Park (take a left Y on that trail when you encounter one, otherwise you end up at a fence at a ballfield). Heading up the hill on a consistent grade you hit a creek crossing. Further up at the top of the hill there is another spur to the left that loops back to the main trail within the next mile, again stay right on the main trail. After the muddy section you cross Grand Ridge Drive. Follow the well-built newer section of trail along the top of Grand Ridge, heading north. After a short distance you pass a trail junction that drops down to the right (this short but wet trail leads to a county road at Grand Ridge Estates, and is a nice loop access to the GR trail via a road that goes up from High Point). Keeping straight on the main trail, the trail Y's again, to follow the newer trail that dives to the right. The next section rises, traverses through a nice forest, then falls steeply to a cedar swamp. The trail appears to end there, but resumes if you cross a small creek and pick it up again on the other side. This section rises slighlty, then flattens and descends, eventually reaching another cedar swamp. The trail once again continues -- follow the rough flat buggy trail to the continuation. Past the flat swampy area, the trail rises from the flats and continues with a climb to Issaquah-Fall City Road.
A nice loop that is easily combined with the Grand Ridge trail involves the trails (roads) on the south side of I-90 at Lake Tradition. This route follows the Issaquah High School Trail up to Lake Tradition and then to High Point, then crosses to the north side of I-90, and then west to the GR trailhead. To do this loop, take a short steep trail up from the Sunset Way parking lot at Exit 18 to get on the former railroad grade that once looped through downtown Issaquah. Take this trail south to near the high school stadium, where the High School trail turns off to the left. (Or, park at the Issaquah Community Center lot - better yet, near the Brew Pub which makes a nice return destination - and ride the paved Rainier Trail to where where it crosses 2nd Ave just south of Issaquah HS, where it turns to dirt. Ride this a short distance until you see the High School Trail taking off to the right). At the high school stadium head up the hill on a dirt road to Lake Tradition Plateau. Once you gain the powerline road at the top, follow it north to the main east-west road, and turn right and ride past Lake Tradition. After hitting the Tiger Mt. parking lot for the hikers, follow the road to I-90 High Point interchange, go under the freeway, and immediately turn left onto the old railroad grade. Follow the dirt road downhill until you hit the main trail leading north up the hill to Grand Ridge. One can get 20+ miles by following this loop, doing an out-and-back to the Duthie Hill Road, and ending up back in Issaquah. And even longer when a link to Soaring Eagle is built.
- GPS track: 
This map (PDF) of the Issaquah Highlands neighborhood also shows the main trail.
Local Points of Interest
One can debate about food, but the best beer in the vicinity as at the Issaquah Brewhouse, which has some 20 taps and many Rogue beers on tap. The Brewshouse is on Sunset Way, just west of Front Steet, Issaquah's main drag. The easiest way to find it coming back from Exit 20 is to take Exit 18, take the Sunset Way split, and go straight until just past the light at Front St.
King County's Mitchell Hill Connector Forest.
KC Parks and WTA are working on a connector trail from near the retention pond down the the trail below the soccer fields. The bridge over the first bog is done but approaches still nee work.
Big trees for a suburban park and only the first part has been overun by invasive plants. One old tree is 24' around.
Keep an eye out for bears
Plans call for flagging a loop up to the water tower this winter. The water tower is north of Grand Ridge Drive. Looks like some good terrain with a nice slope. Also talk of adding rails to the skinny bridge.
There was a battle with in KC Parks about this trail being open to bikes. It's important to show the county we care by showing up for work parties. http://wta.org/~wta/cgi-bin/wtaweb.pl?6+tt Also the Highlands home owners asc. has been doing some work here and there.