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All About ‘The Sinks’

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A picturesque, natural sandstone formation in Limestone Canyon has become a popular destination for outdoor enthusiasts.

In the southern portion of OC Parks’ Limestone Canyon Nature Preserve sits “The Sinks,” a striking geological formation consisting of dramatically exposed and layered sandstone cliffs. The raised viewing platform that overlooks an impressive view of The Sinks has become a popular destination for explorers of the Irvine Ranch Natural Landmarks. While the beauty of The Sinks is instantly understood by all who visit, the history of the formation is millions of years in the making


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The red sandstone cliff faces of The Sinks are part of the Sespe Formation, a geologic area of southern California which is aged between 20-40 million years old. The Sespe Formation is more resistant to erosion than many other regional sedimentary rock formations, which, over millions of years has resulted in the creation dramatic outcrops and ridgelines in a number of local mountain ranges. The formation of the Sinks’ dramatic amphitheater shape was likely due to episodes of landslides and stream erosion over several million years— natural processes which continue to shape this living geological feature.

The Sinks is situated at the top of the Agua Chinon basin, a 1,200-acre canyon that is part of the San Diego Creek Watershed that bisects OC Parks’ Limestone Canyon Nature Preserve. The Sinks is most often accessed, during scheduled programs and Wilderness Access Days, from the Augustine Staging Area, which is just less than 4 miles (8 miles round trip) from The Sinks viewing deck. From the staging area, visitors will travel southeast along the sandy Limestone Canyon Trail as it meanders through open meadows and several shaded oak groves, gradually gaining elevation.

Whether on foot, mountain bike or horseback, visitors will then arrive at a short path leading to a wooden platform, built by the Irvine Ranch Conservancy field operations team in 2011, which looks out over The Sinks and sprawling vistas beyond. From the viewing deck, people can see the ground drop off sharply into the canyon below while impressive sandstone walls create a kind of a natural bowl.

The topography, and the deep cavity of The Sinks, creates a consistent breeze in the area as wind travels up over the cliff faces of The Sinks. This has a nice cooling effect in warmer months, and makes it a great place to watch soaring hawks and turkey vultures as they ride on thermal waves of air above the cliffs. Lucky visitors might also catch a glimpse of a grey fox climbing the cliff walls, mule deer feeding on the shrubs of the canyon floor below or lizards darting around the edges of the rocky hillside.

As more and more people learn about The Sinks, and its reputation as “Orange County’s miniature Grand Canyon” continues to grow, guided activities and Wilderness Access Days will continue to bring hikers, trail runners, mountain bikers, equestrians and photographers to this unique natural formation. If you haven’t yet had the opportunity to visit The Sinks, or if you’re interested in planning a return trip, there are plenty of upcoming opportunities.

On the morning of Thursday, April 30, hikers can participate in the Morning Nature Hike in Agua Chinon. This 7-mile hike will travel up the Agua Chinon watershed and continue on to The Sinks. A couple weeks later, on the morning of Wednesday, May 13, hikers can visit The Sinks during the Mid-Week Hike—Agua Chinon, a 12-mile hike with 2,100 feet of accumulated elevation climb.

Trail runners can join docents for a 12.5-mile run through OC Parks’ Limestone Canyon Nature Preserve during the Trail Run Agua Chinon to The Sinks and Limestone Canyon on the morning of Saturday, May 23.

Mountain bikers can visit The Sinks during several upcoming rides in OC Parks’ Limestone Canyon Nature Preserve. On the morning of Sunday, May 3, the Intermediate Mountain Bike Ride from Hicks Haul Road to Limestone Canyon will travel along paved Hicks Haul Road, climbing up to Loma Ridge, before descending into the dirt trails of Limestone Canyon. On Tuesday, May 12, mountain bikers are invited to join the 12-mile Intermediate Evening Mountain Bike Ride for a chance to see Limestone Canyon and The Sinks in the fading light of early evening.

Equestrians can visit The Sinks on the morning of Friday, May 15 during the monthly Limestone Ride to the Sinks. This leisurely 8-mile ride will travel along the Limestone Canyon Trail.

If you would prefer to hike or ride to The Sinks on your own, and at your own pace, consider attending the next Wilderness Access Day in Limestone Canyon, on Saturday, June 6. This is when the public has the opportunity to access designated trails in OC Parks’ Limestone Canyon Nature Preserve between 8:00 am and 2:00 pm. The average hiker will be able to hike the 8-mile round trip from the Augustine Staging Area to The Sinks and back in about 4.5 to 5 hours. Fast hikers might make it in 3.5 hours. If you are planning to make the journey during a Wilderness Access Day, please arrive early (before 9:00 am)—giving your group plenty of time for the hike.

Click here to be taken to a full list of upcoming hiking, trail running, mountain biking and equestrian activities in Limestone Canyon that will make a stop-off at The Sinks.

These programs are free and require pre-registration for all participants (children must attend with their parent or guardian). Wear comfortable shoes and bring plenty of water. To find out more information about other offered programs, please visit www.LetsGoOutside.org/activities.