Is this open these days? And what are the timings?

You must sign up for available hikes @ let's go outside. Every person wishing to hike must sign up, spaces are limited, many hikes are docent lead but there are occasional 'open days' when registered hikers/bikers/horseback users roam the trails without a docent. Spaces are limited, example there are 2 spaces left for June 21 docent lead as I write

In 2006 Limestone Canyon became part of the first National Natural Landmarks and in 2008 they were named California Natural Landmarks. You can go hiking (biking and horseback riding too) on the Landmarks via free guided programs offered through the Let's Go Outside website. The Irvine Ranch Conservancy takes care of the Landmark properties.