Thunder Lake - Lion Lake Loop, Wild Basin Trailhead, Rocky Mountain National Park, Colorado

Thunder Lake - Lion Lake Loop - 15.5 miles

Wild Basin Trailhead

A large, unnamed tarn between Thunder Lake and Lion Lake

A large, unnamed tarn between Thunder Lake and Lion Lake

Round-Trip Length: 15.5 miles (distance will vary by route)
Start-End Elevation: 8,510' - 11,570' (11,570' max elevation on route)
Elevation Change: +3,060' net elevation gain (+3,575' total elevation gain)
Skill Level: Strenuous
Dogs Allowed: No
Bikes Allowed: No
Horses Allowed: No
Related Trails:

Thunder Lake - Lion Lake Loop - 15.5 Miles Round-Trip

A short but challenging cross-country segment connects Thunder Lake, Snowbank Lake and the Lion Lakes in Rocky Mountain National Park. The clockwise route follows a well-maintained trail to Thunder Lake (5.8 miles), then veers north on a steep off-trail climb that levels across stunning alpine flats between drainages.

Trail Map | Photo Gallery

A social trail picks up at Snowbank Lake (7.95 miles) that drops to Lion Lake #2, Trio Falls and Lion Lake #1 (8.75 miles), where maintained travel resumes back to Wild Basin to complete the 15.5 mile lollipop loop.

Off-trail (and therefore, total) distance will vary by individual route; if short on time or pressed by weather, Snowbank Lake and Lion Lake #2 can be excluded.

The off-trail segment described here is about 1.9 miles, which can be shortened by taking a more direct line between drainages that might skip some interesting features.

Though this description travels clockwise, it's arguably easier (and depending on weather, wiser) to travel counter-clockwise and tackle Lion and Snowbank first.

This approach takes advantage of maintained / good social trails to the route's highest points, and descends (rather than climbs) the steepest section above Thunder Lake.

Consider your ability, weather status and potential snow cover to inform your decision. Good map reading and navigation skills are essential, whichever direction you go. Only experienced hikers should attempt this route. 

While its 4 lakes are compelling enough, airy alpine flats and pristine tarns between them are the route's true highlight. Tread lightly when off-trail, walk on rock slabs whenever possible and avoid trampling sensitive alpine vegetation.

To expedite travel, this description uses the Backcountry Campsite Access Trail vs. following the main trail all the way to Thunder Lake (see map).

Doing so skips Calypso Cascades and Ouzel Falls, but reduces roundtrip mileage by 1.5 miles and saves valuable time for more demanding and exposed sections ahead:

The trail rises gently beside North St Vrain Creek past spurs for Lower and Upper Copeland Falls (.35 and .45 miles) to the backcountry campsite access trail split (1.38 miles : 8,860').

Bear right on a variously steep and rocky climb past the Tahosa and Aspen Knoll Campsite spurs to rejoin the main trail (2.65 miles : 9,505'). Grades moderate on a fast and nondescript stretch to the Thunder Lake - Lion Lake Trail split (3.9 miles : 10,025').

The Thunder Lake Trail steepens through a subalpine forest with views of Mertensia Falls across the valley to a bridge (5.05 miles : 10,510').

It rises to a crest at the Thunder Lake Group Campsite spur (5.65 miles : 10,676') and drops to the Ranger Cabin at Thunder Lake (5.8 miles : 10,574').

A well-defined trail continues along the north side of Thunder Lake to a bridge over the inlet (6.05 miles). Don't cross the bridge; veer right here and follow the north fork of the inlet stream into the forest. A faint path continues up this prong a short distance before fading on a steep slope in a cluttered forest. 

Stay NE of the stream and work your way up the slope (note that you can follow the stream to good views of Fan Falls, but it will add distance and difficulty).

This tough climb rises 630' in just .5 miles through treeline with exceptional views over Thunder Lake before leveling out to a large tarn (6.65 miles : 11,240'), whose outlet forms Fan Falls below.

Travel eases considerably here, and you'll be free to explore this notably attractive and rarely seen expanse between drainages. 

Follow best available terrain north to a second tarn (7.1 miles : 11,370'), then scale a ridge to a high point between Lion Lake #2 and Snowbank Lake (7.65 miles : 11,590'). If pressed for time, stay low and follow gentle terrain NE down to the south side of Lion Lake #1.

Drop to Snowbank Lake (7.95 miles : 11,523'), then turn back east on a social trail down to Lion Lake #2 (8.25 miles : 11,413'). Continue down beside Trio Falls to Lion Lake #1 (8.7 miles : 11,075'), and cross the inlet to pick up the maintained trail along the north shore.

The maintained trail drops on a steep, shifting path back to the Thunder Lake - Lion Lake split (11.6 miles). Retrace your steps back to Wild Basin to complete the hike (15.5 miles ).

Illustration of bighorn sheep

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Interactive GPS Topo Map

Key GPS Coordinates - DATUM WGS84

  • N40 12.469 W105 33.993 — 0.0 miles : Wild Basin Trailhead
  • N40 12.230 W105 34.391 — .45 miles : Spur to Upper Copeland Falls
  • N40 12.022 W105 35.293 — 1.35 miles : Backcountry campsite access trail split
  • N40 11.923 W105 35.540 — 1.7 miles : Tahosa Campsite spur
  • N40 12.094 W105 35.839 — 2.0 miles : Aspen Knoll Campsite spur
  • N40 12.304 W105 36.407 — 2.6 miles : Rejoin main trail; bear right
  • N40 12.490 W105 36.960 — 3.15 miles : Fast, moderate travel
  • N40 12.773 W105 37.495 — 3.9 miles : Thunder Lake - Lion Lake Trail split
  • N40 12.808 W105 37.910 — 4.4 miles : Transition into subalpine forest
  • N40 13.236 W105 38.233 — 5.05 miles : Cross bridge over tributary
  • N40 13.343 W105 38.691 — 5.8 miles : Thunder Lake (10,574')
  • N40 13.429 W105 38.962 — 6.05 miles : Cross Thunder Lake inlet stream
  • N40 13.514 W105 39.068 — 6.25 miles : Steep climb along inlet tributary
  • N40 13.621 W105 39.039 — 6.35 miles : Steep climb in cluttered forest
  • N40 13.736 W105 39.029 — 6.45 miles : Steep climb in thinning forest
  • N40 13.783 W105 38.992 — 6.55 miles : View from open slope over Thunder Lake
  • N40 13.810 W105 39.051 — 6.65 miles : Large tarn above Fan Falls
  • N40 14.027 W105 38.897 — 7.05 miles : Cross high level flats
  • N40 14.107 W105 38.930 — 7.1 miles : Wrap around tarn
  • N40 14.120 W105 38.666 — 7.6 miles : Ridge over Snowbank Lake
  • N40 14.375 W105 38.690 — 7.95 miles : Snowbank Lake
  • N40 14.234 W105 38.467 — Lion Lake #2
  • N40 14.104 W105 38.350 — Cross nlet to north shore of Lion Lake #1
  • N40 13.924 W105 38.284 — 8.1 miles : Lion Lake #1
  • N40 13.425 W105 38.101 — Fast, shifting descent
  • N40 13.051 W105 37.929 — Fast descent through treeline
  • N40 12.930 W105 37.675 — Steep, shifting descent in subalpine forest

Worth Noting

  • A detailed map is essential for safe and efficient off-trail travel between drainages.

Camping and Backpacking Information

Backcountry Camping in Rocky Mountain National Park

  • A permit is required for all backcountry camping in Rocky Mountain National Park. Permits may be obtained from the Beaver Meadows Visitors Center Backcountry Office, or the Kawuneeche Visitor Center at Grand Lake. Day-of-trip permits may be obtained in-person, year round.
  • There's a $26 fee to backcountry camp in Rocky Mountain National Park (May 1 - October 31). This administrative fee covers each party (defined as an individual or group) for the duration of the trip. Note that park entrance fees are applied separately and in full.

Backcountry Campsites in the Wild Basin Area

Pine Ridge Backcountry Campsite

  • The Pine Ridge site is located 1.4 miles from Wild Basin Trailhead at 8,880'. There are 2 individual sites and a privy. 2 backcountry sites are located in a lodgepole forest north of the trail, just east of the bridge across North St. Vrain Creek. A food storage cable is about 8 steps past the spur to site #1. It's in a small clearing to the left and runs perpendicular to the trail. Obtain water from North St. Vrain Creek.

Tahosa Backcountry Campsite

  • The Tahosa site is located 1.7 miles from Wild Basin Trailhead at 9,040'. There is 1 individual site and no privy. The site is .3 miles up the unimproved backcountry campsite access trail in a lodgepole stand at the edge of a small rocky bluff. Obtain water from N. St. Vrain Creek, approx. 160 yards downhill from the site.

Aspen Knoll Backcountry Campsite

  • The Aspen Knoll site is located 2.0 miles from Wild Basin Trailhead at 9,400'. There is 1 individual site and no privy. The site is located along the unimproved backcountry campsite access trail in a mixed aspen-pine forest. Obtain water from North St. Vrain Creek, approximately 200 yards downhill from the site.

Siskin Backcountry Campsite

  • The Siskin site is located 3.2 miles from Wild Basin Trailhead at 9,460'. There is 1 individual site and no privy. The site is located along the unimproved, backcountry campsite access trail in a lodgepole stand. Obtain water from North St. Vrain Creek, approx. 135 yards downhill from the site.

North St Vrain Backcountry Campsite

  • The N. St Vrain site is located 2.65 miles from Wild Basin Trailhead at 9,560'. There are 2 individual sites and a privy. The sites are located along the unimproved backcountry campsite access trail, right where it rejoins the main trail. A food storage cable is located 20 steps up the access trail in a small clearing on the left, and parallel to the trail. The sites lie in a thick lodgepole stand on the north side of the trail, just after it crosses N. St. Vrain Creek. Obtain water from the creek.

Thunder Lake Backcountry Campsite

  • The Thunder Lake site is located 6.8 miles from the Wild Basin Trailhead at 10,574'. There are 3 individual sites, 1 group site and 1 stock site. The individual sites are located in a forested area north of the trail about 300 yards east of the lake. The stock site is about 100 yards from the lake on the south side of the trail and slightly east of the hitchrack. Obtain water from Thunder Lake's outlet stream.

Fishing Information

A valid Colorado fishing license is required for all persons 16 years of age or older to fish in Rocky Mountain National Park. No other permit is necessary; however, special regulations exist. It's your responsibility to know and obey them. 

Due to the dynamic nature of fisheries management, fishing regulations can change at anytime. Special closures may be put in place above and beyond what is listed here. Contact the park before heading out for current information.

  • Method of Capture: Each person shall use only one hand-held rod or line. A 'second rod stamp' is not honored in park waters. Only artificial lures or flies with one (single, double, or treble) hook with a common shank may be used. "Artificial flies or lures" means devices made entirely of, or a combination of, materials such as wood, plastic, glass, hair, metal, feathers, or fiber, designed to attract fish.
  • This does not include: (a) any hand malleable material designed to attract fish by the sense of taste or smell; (b) any device to which scents or smell attractants have been externally applied; (c) molded plastic devices less than one and one-half inch in length; (d) foods; (e) traditional organic baits such as worms, grubs, crickets, leeches, minnows, and fish eggs; and (f) manufactured baits such as imitation fish eggs, dough baits, or stink baits. Fly fishers may utilize a two hook system, where one hook is used as an attractant.
  • While in possession of any fishing equipment, bait for fishing (insects, fish eggs, minnows, or other organic matter) or worms is prohibited. Children 12 years of age or under, however, may use worms or preserved fish eggs in all park waters open to fishing except those designated as catch-and release areas.
  • No bait or worms are allowed in catch-and-release waters.
  • Use of lead sinkers (or other lead fishing materials) is strongly discouraged.

Rules and Regulations

  • A $20 Day Use Fee is required to enter Rocky Mountain National Park (or $30 for a 7 Day Pass).
  • Dogs are not permitted on hiking trails in Rocky Mountain National Park.

Directions to Trailhead

The Wild Basin Trailhead is located 2.3 miles west of Highway 7 between the towns of Allenspark and Estes Park.

From Estes Park, head south on Highway 7 for 11 miles to the Wild Basin turnoff on the west side of the road. Turn west on the dirt road to the entrance station .15 miles ahead. The Wild Basin Trailhead is located 2.15 miles from the entrance station. Parking is limited, and roadside restrictions are strictly enforced.

Contact Information

Rocky Mountain National Park
Visitor Information:
970.586.1206

Backcountry Office:
970.586.1242

Campground Reservations:
800.365.2267

Trip Reports

There are no trip reports on this trail.



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