Boulder, CO: Gross Reservoir

Explore tiny lakeshore beaches (and don’t forget your fishing pole) on this 3-mile trek that heads cross-country on the southeast corner of Gross Reservoir.
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Gross Reservoir rests in the South Boulder Creek drainage and is an easy-access Front Range destination for paddling and fishing. This short hike begins at Osprey Point and follows the first 0.25-miles of the well-worn Inlet Trail. You’ll climb a small hill and drop into a ravine where this route turns right and off-trail to cruise above rock lined beaches. Depending on the level of the water, it’s either easy-going along the beach or a cross-country traverse of the hillside above the shoreline like this route shows. Deer trails criss-cross the pine and juniper-covered slope but even if you're on the beach most of the time, expect to pick your way up over fallen trees when you turn uphill.

The northernmost point of this route rounds a peninsula and climbs a steep hillside to a hilltop overlook of the creek inlet. Cruise the forested ridgeline south and re-connect with the trail headed east. Trail markers and rocky steps lead to a shaded picnic area and a few hundred feet further to gentle rapids and lounging rocks along the creek.

While there are a few rough sections and steps on the trail itself, most hikers use it as an out-an-back which is easier than this route’s cross-country approach.
-Mapped by Kristy Holland

Trail Facts

  • Distance: 4.8



Location: 39.9367241, -105.3728342

The Inlet Trail heads uphill from the parking area where you'll also find toilets, picnic tables and plenty of parking.


Location: 39.9349801, -105.3754091

After crossing the first ravine, this route takes a deer path to the right, just above the lake and heads cross-country along the shoreline. If you'd rather stick to the trail, look for small reflective markers on the trees and stay uphill to the left after passing the blue trail marker.


Location: 39.9398665, -105.3834558

Some sections of shoreline are steep and loose. If the beach isn't wide enough to walk on, pick you way up deer paths and follow trails traversing the hillside.


Location: 39.9395539, -105.3849149

From the top of the hill there's a view of the inlet and the east side of the reservoir. Follow the ridgeline south from here about 200 yards to the trail.


Location: 39.9375385, -105.3842926

The trail is easy to spot in the open pine forest. Heading east from this point it descends about 200 feet to the South Boulder Creek inlet.


Location: 39.9372752, -105.3886592

There are a couple of large rocks, perfect for relaxing on, at hike end. Though you'll likely see fly fishermen near this point, keep in mind that swimming is prohibited.


Location: 39.9374891, -105.3841907

After climbing to the ridgeline from the inlet, stick to the main trail for the return trip. You'll roll through a couple of drainages and catch far-off mountain views on the easy-to-follow path.


Location: 39.9353996, -105.3777105

Though the elevation changes are slight, pay attention to your footing on a steps and a couple of loose, steep sections of the trail over ridges and into ravines.


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Follow the trail to the right of this sign at the trailhead picnic area.


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Walking uphill on the from the trailhead picnic area with the reservoir in the background.


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Looking east across the first inlet toward the trailhead and boat launch at Osprey Point.


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Occasional trees alongside the South Boulder Creek Inlet Trail are marked with reflective tape.


Location: 39.9352886, -105.3775281

Some parts of the trail climb loose, rocky steps. Watch your footing.


Location: 39.9361647, -105.3810954

The waterline of the reservoir fluctuates, but in early summer, expect the shoreline to nearly touch the trees.


Location: 39.9370655, -105.3854996

The South Boulder Creek Inlet Trail is also marked by blue carsonite signs as you approach the creek inlet.

Lean To

Location: 39.9370696, -105.3879189

Just south of the creek, this makeshift shelter is a great place to have a meal or relax if it's very windy near the water.

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