Today the Irish Hills are like a gold mine for hikers, but the small mountain range in San Luis Obispo historically hosted several mines for chromium and mercury. The ruins of one of these mines can be visited on Old Prospector Trail, which opened in 2015 to join the growing group of trails in Irish Hills Natural Reserve. This hikers-only single track starts in Froom Canyon and is 0.9 miles long from end to end. Alongside the ruins of the mining operation at the top of Old Prospector Trail, there is a junction with Wednesday Trail (formerly Pond Trail), which can be used to reach the Johnson Ranch – Irish Hills Connector Trail and form a loop for a hike that’s 3.4 to 4.4 miles round trip with 650 feet of elevation change. Put the Old Prospector to work on this less-explored loop in the Irish Hills!
The bottom of Old Prospector Trail is located in Froom Canyon, 0.5 miles from the nearest trailhead in a shopping area alongside the Irish Hills. Starting from the more formal Madonna Trailhead at the end of Madonna Road, it is one mile to the beginning of Old Prospector Trail.
Setting out from Madonna Trailhead, make an immediate left onto King Trail. The single track crosses a grass slope and comes to a junction with Froom Creek Trail, just over a quarter mile from the start. Turn left again and pass through a pocket of oaks. Froom Creek Trail crosses more grassy slopes with views to the left over Costco and other developments along Los Osos Valley Road. A 0.15-mile long trail joins Froom Creek Trail on the left, coming up from the Costco Parking Lot. Starting from the Costco Parking Lot, hike up this dirt trail and turn left on Froom Creek Trail, passing over livestock steps just past the junction. Froom Creek Trail rounds a bend and descends into Froom Canyon, reaching a junction at the bottom of Froom Canyon in another tenth of a mile. Instead of hiking up the canyon on Froom Creek Trail, bear left onto the Connector Trail, which ventures all the way to Johnson Ranch.
Cross the bottom of the canyon and head up the opposite side through oaks and brush. After a quarter mile, the trail makes a sharp horseshoe bend to the left and prepares to climb out of the canyon. Old Prospector Trail begins on the outside of this bend, maintaining the same course up the south side of Froom Canyon.
Unlike the many mountain bike-friendly trails in Irish Hills Natural Reserve, Old Prospector Trail is open to hikers only and has a less-used feel. Sections of the trail follow the bed of an old road that has been overgrown and eroded. An excellent rugged quality has been retained with the construction of this new trail over a historical route.
Old Prospector Trail goes along the side of the canyon across from Froom Creek Trail for 1/8 of a mile and then makes a sharp left turn up stone steps to climb out of the canyon. The trail rounds a bend into a side canyon that branches off of Froom Canyon.
The trail is narrow as it crosses the steep side of the ravine. Look down on a seasonal stream that flows down the ravine through boulders and a thicket of brush. Cross this creek just over a quarter mile from the start of Old Prospector Trail and make a U-shaped bend to head up the other side of the ravine. Old Prospector Trail ascends chaparral-covered slopes, attaining views looking down Froom Canyon toward San Luis Obispo. The trail rounds the end of the ridge for views up the main trunk of Froom Canyon. Rising above the far side of the canyon, the tops of Bishop Peak and Cerro San Luis appear.
After a horseshoe bend, Old Prospector Trail heads south across the slopes at the top of the side canyon, aiming for the higher terrain above. As it leaves the steepest part of the canyon, the trail curves to the right around one last gully at the top of the canyon. Look across this gap toward the ruins of an old mine. A retaining wall, broken pillars, and a concrete footprint remain from an old mining claim. Mine Hill rises behind the old mine above the ravine. To get closer to the mine, continue to the end of Old Prospector Trail.
Old Prospector Trail ends at a T-junction with Wednesday Trail, which was formerly called Pond Trail. The trail had taken its name from a nearby reservoir, but now the name recognizes the trail builders that gathered on Wednesdays to make trails in the Irish Hills. Old Prospector Trail gained 560 feet of elevation over 0.9 miles to reach this point, 1.4 miles from the Costco Trailhead and 1.9 miles from the Madonna Trailhead. Turn left here to continue with the loop, but first stray a few steps to the right to get a good view of the old reservoir that was part of the mining operation. Note: You could also reach the Johnson Ranch – Irish Hills Connector Trail by turning right on Wednesday Trail, hiking higher into the Irish Hills.
After turning left on Wednesday Trail, you will immediately pass through the ruins of the old mine, hiking right by an old wall that appears to have been built to create the reservoir for the mining operation. Mirroring Old Prospector Trail, Wednesday Trail takes a course along the other side of the ravine. A curve into a draw to the right leads to a small grove where there is a bench beneath a large tree that is ideal for a quick break in the shade. The bench is a quarter mile from the top of Old Prospector Trail. For here, Wednesday Trail continues another 0.45 miles down to a utility road. The single track trail crosses low brush that allow hikers to survey the route of Old Prospector Trail on the opposite side of the ravine. There are also views looking up at Mine Hill, down on Froom Canyon, and over the surrounding Irish Hills.
Turn right when you reach a dirt road, 0.7 miles from the top of Old Prospector Trail (and 2.1 or 2.6 miles from the start of the hike). Walk down this dirt road for 300 feet to a junction with another dirt road. This is Johnson Ranch – Irish Hills Connector Trail. Meet the Connector Trail at a horseshoe bend and turn left to head back toward Froom Canyon.
After a tenth of a mile on Johnson Ranch – Irish Hills Connector Trail, you will pass a single-track trail that break off to the left. This trail can be used as an alternative to the next 0.35 miles of the Connector Trail. It is 0.75 miles long, packed with switchbacks, and popular with mountain bikers. Bikers call this trail Chutes and Ladders Trail and it provides a gentle grade with additional views over Froom Canyon (and can be used to extend the hike by 0.4 miles).
Sticking with the main trail, there are views east over Edna Valley that expand north toward San Luis Obispo as the road curves to the left around the mountainside. Just past the bottom of Chutes and Ladders Trail, the Connector Trail comes to a junction at a saddle near the end of the ridge. You have the option to turn right or left here for equidistant routes to the bottom of Froom Canyon.
The jeep road to the right, which is called Neil Havlik Way, curves around the bottom of the ridge and becomes faint. At the end of the ridge, turn left to walk up to Froom Creek Trail.
The more obvious choice is probably to turn left, cross the saddle, and hike down into Froom Canyon. Enjoy views over the canyon before descending into oaks. At 0.3 miles from the saddle, the trail makes a sharp bend to the right and passes the start of Old Prospector Trail. You have closed the loop, returning to this point 2.4 miles after you left it. Continue down the trail for another quarter mile and cross the creek bed to the junction with Froom Creek Trail. From here it is a quarter mile back to the Costco Parking Lot and 3/4 of a mile to the Madonna Trailhead. Return to wherever you started from for a 3.4 or 4.4–mile hike.
Bikes are not allowed on Old Prospector Trail, but every other trail along this loop is bike-friendly. Hikers are welcome to bring dogs on leashes. Those wishing to hike farther could connect this loop to other trails in the Irish Hills (like Froom Creek Loop). No fee or permit is required to hike in Irish Hills Natural Reserve, so get out and enjoy!
To get to the Madonna Trailhead: Take Highway 101 to exit 200, Los Osos Valley Road, three miles south of downtown San Luis Obispo. Drive northwest on Los Osos Valley Road for one mile and turn left on Madonna Road. Drive 1/3 of a mile to the intersection at the end of the road and park. The trail continues from the end of Madonna Road. There is a short paved walkway between houses up to a map of the park at the junction with King Trail.
Trailhead address: Madonna Road & Devaul Ranch Drive, San Luis Obispo, CA 93405
Trailhead coordinates: 35.254311, -120.69525 (35° 15′ 15.51″N 120° 41′ 42.90″W)
To get to the Costco Parking Lot: Take Highway 101 to exit 200, Los Osos Valley Road, three miles south of downtown San Luis Obispo. Drive northwest on Los Osos Valley Road for half a mile and turn left into the shopping complex. The trail begin at the end of the road near the queue for the Costco gas station.
Trailhead address: 1540 Froom Ranch Way, San Luis Obispo, CA 93405
Trailhead coordinates: 35.25054, -120.69115 (35° 15′ 01.94″N 120° 41′ 28.13″W)
|Froom Creek Trail Loop
This 3-mile loop explores a canyon on the east side of the Irish Hills, ascending 500 feet to a nice view over Laguna Lake, Cerro San Luis, and Bishop Peak.
This 3.15-mile hike in the Irish Hills Natural Reserve delivers panoramic views over Los Osos Valley and the full chain of Morros.
|Johnson Ranch Loop
This 2.5 to 3.7-mile loop explores a grassy open space just south of San Luis Obispo.
|Johnson Ranch - Irish Hills Connector Trail
This scenic 5-mile point-to-point hike connects Johnson Ranch Open Space with Irish Hills Natural Reserve.
|South Hills Ridge Trail
This 1.5-mile round trip hike ascends 425 feet to the highest point in a cluster of hills near downtown San Luis Obispo, offering fine views over the city and surroundings.
|More hikes in San Luis Obispo
Explore other trails around San Luis Obispo including Morro Bay State Park, Montaña de Oro State Park, and the Morros.