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Level: Advanced
Length: 30 mi (48.3 km)
Surface: Singletrack
Configuration: Loop
Elevation: +825/ -809 ft
Total: 56 riders

Mountain Biking The Underdown

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#24 of 387 mountain bike trails in Wisconsin
#1,072 in the world

The Underdown is a gem of a trail system that has extensively changed from a handful of years ago. If you are looking for a rugged back country style ride with lots of technical singletrack with very little doubletrack networking, this is for you. There are now two trail heads, the main north trail head located off of Copper Lake Road northeast from the City of Merrill, nearest to Lincoln Hills correctional facility. Straight out of the north parking lot into the woods you hit singletrack that combines climbing with equal length downhill shots. For some 1x1 riders you might find yourself walking most of the climbs if you're not ready for them. Be prepared for some loose rocks, off camber runs with switchbacks, wet root sections and sweet downhills. There are also a number of nice bridges, boardwalk features along the trail. I've found that the knobbier the tire, the better. Updates in 2017 have brought a bit of machine built reconstruction to some of the interior trails to add a bit of flavor to the entire system.

The second southern trail head is off of County Hwy R/Heineman Road in the City of Merrill Memorial Forest. The trail head at this time is nothing more than a grassy parking area and has NO drinking water or restrooms so be prepared. Head south around the metal gate for about 1/4 mile and you will access the Prairie Dells loop. A fun, easy 5 mile loop that highlights itself at the Prairie River Dells overlook about halfway through the loop. This trail is primarily machine constructed single track with a touch of double track. Plenty of climbing but not as severe as the northern Underdown area and all of the climbs are rewarded with fast, flowing downhills and berms.

Heading north from the Prairie Dells trail head you can link up to the Underdown trails via the Connector trail, another machine built gem with lots of good flow, berms and some jumps. Access the connector trail from a double track entrance on the north side of the road right where the County Hwy R pavement ends into gravel road. Scoot around a cable gate and the single track shoots up the first ridge. Heading north for the next 2.3 miles you will primarily climb with a few short downhill rewards. But after you have ridden some loops on the Underdown interior head back down the connector for some really fun longer downhills with only short uphill sections.

For a big day in the saddle combine the main outer perimeter of the Underdown with the Prairie Dells loop and you have about 30 miles of riding.

Overall the singletrack trail system is perfectly maintained (even in the fall) and is marked very well.
For more trail info check out: http://thunderdown12.blogspot.com/

First added by Danno#1 on Jan 11, 2009. Last updated May 11, 2020. → add an update
Before you go
  • Drinking water: unknown
  • Lift service: unknown
  • Night riding: yes
  • Pump track: unknown
  • Restrooms: yes
  • Fat bike grooming: yes
  • E-bikes allowed: unknown
  • Fee required: unknown
This trail information is user-generated. Help improve this information by suggesting a correction.
Getting there
45°19'47.39"N, 89°35'7.46"W
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The Underdown Trail map

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mblock78 (on May 30, 2021)
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Underdown Recreation Area: Connector/Disconnector
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  • hollyanne99

    One of the best trail systems in WI! For intermediate to advanced riders in terms of endurance/rocky riding. Not large chunky rocks, but old-school, wear-you-down constant bumpy riding. You need to be fit to string together a length of trail here. However, the riding offers some lake views and has many punchy climbs. Sections C/CC and S/TT were my favs, and then I discovered the connector trail. The connector trail is at the far end of the system or accessible from another parking area and is very fun flowing trail (not so old-school). I rode in both directions and thought it was a blast. This trail gets very little mention as a destination, but I think it is one of the best offering 2-3 days of riding!

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  • LarvaRabbit

    Great trail system. Single track trails are tough, but the scenery is fantastic and there are miles to choose from. Signage is mostly pretty good. One of my favorites places.

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  • stumpyfsr   ✓ supporter

    This trail is very similar to Rock Lake or Nicolet National Forest. It's a constant workout over rocks and roots. It's very well marked yet the layout is a bit confusing in places because it intersects with other trails, which add some adventure feeling to your ride.

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  • rcneumes

    RIDE THIS TRAIL! If you think to yourself "hmm I think I will go ride Nine Mile" STOP YOUR THOUGHT! Instead go ride The Underdown. So much fun! Climbs are rewarded with insane roller and switchback sections. Awesome use of the terrain.

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  • OTB-bOb

    Awesome trail system but a butt kicker so be prepared!! A true gem and pretty easy to link almost 30 miles of singletrack together if you have enough time. Nothing over technical but a great workout for the legs and upper body as well. One of the best systems in WI for sure,

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  • Jesse Eilbes

    Nice tight trails, very challenging.
    Lots of up and down hills, very well planned and marked.

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  • davver

    I'm giving this trail a 3, but I want to ride it again. It was 85 degrees and humid the day I went and between the hills and the heat it was very tough aerobically. The trails are very rideable if you know how to ride up a hill that has roots and rocks. The down hills are very manageable, but not long enough to catch your breathe. The trails are marked very well and there are spots that you can jump off the trail back to the main road. It is very isolated so don't plan on lots of company on the trail. Lastly, there is a $5 trail fee.

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  • Russm

    Definitely an advanced trail. Wear repellent. Pretty technical with some tough climbs, lots of roots and some overgrowth. Downhills didnt provide much reprieve as they were pretty technical. If you like flow and speed, this isn't the trail for you, if you like roots, rocks and and a challenge, check this trail out. Wear repellent though. Also, the maps were tricky and trail head was hard to find.... When you are looking at the "parking lot" from the road, the trailhead is at the back right of the open space. Also wear repellent.

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  • Kelly Longtine

    The Underdown is one of the best! It will challenge you physically no doubt but there is enough places to recover if you know how to. The trails have always had a reputation as raw, rustic and remote. That is still true but recent years have brought a few new treats to the trail like bridges, boardwalks, flow sections, berms and Chris the trail ninja and crew have worked endless hours on tweaking and maintaining to improve the trail as a whole. New maps, and signage has also improved recently. If you go bring water and be prepared. There is also some Snow/Fat bike opportunities in winter. Snowshoeing here is awesome as well.

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  • jrerickson724

    Rode this years ago with my brother in law. I think they added a lot of distance since then and a lot of bridges. Fantastic trail. Reminds me of West Virginia single track. They like to call natural cut trail. This wasn't quite like that but not far off. Very fun to ride. Very scenic.

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  • Charlie29

    This place is awesome! A definite must ride! Very fun single track with a good amount of technical/challenging areas. Definitely one of the best trails in Wisconsin in my opinion.

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  • rmac78

    This place is fantastic. Kudos to all the people who work on these trails, you guys do a great job. The scenery is beautiful. There are a lot of great sections with water crossings and awesome whoop sections to really pick up some momentum. I live close by now and plan on being a permanent fixture among these trails. Always wear plenty of bug spray as others have mentioned.

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  • Chris Daniels

    This trail system has it ALL! I agree with all other reviews and will add to them of the primitive nature of this place. As you work your way deeper into the woods, the trail is over grown, you're constantly brushing the encroaching bushes, and the bugs just get weird! It's almost scary how ancient this place feels... and it's all a good thing. If your in the area, it would be a serious mistake to not hit this. You can make it a quick loop, but to get the most I would plan on about 2:30. And as others, don't just dowse the spray on at trailhead, lay it on thick and take it with you!

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  • edl419

    Awesome trails. bring lots of bug spray or the mosquitoes and/or horseflies will carry you away

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  • PaulMiller

    The trails are fun but dont go in the summer alot! of bugs. had 20 ticks on me in the 1st hour.wore 40%deet the bugs laughed at it.

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  • Thunderdown12

    As the builder on this system, I thought I should direct you to the trail's website: http://thunderdown12.blogspot.com/

    The next race is July 3rd, 2010

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  • Alistair19

    Once I found the trail (small trail markers) the 2 hours I had to spend seemed like it was over in a second. Trail A starts out with simple climbs, and transitions into a fun down hill. Trail B is similar to A except alot more rocks & roots to be technical around and just when you start getting the hang of this place.. Trail C nails you with some serious hill sections. I highly recommend this place and can't wait to go back!

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