Sage Ranch Park is a hidden gem nestled within the mountains between Simi Valley and Chatsworth. Managed by a conservancy organization, it is open for day use ($5 parking) and reserveable for camping.
There is a hiking loop of about 3 miles that encircles the park, with great views all around. Here you will also see a glimpse of the former Rocketdyne plant, which was the site of the worst nuclear disaster in US history.
My son did an eagle scout service project here, and we've camped here many times.
It's a very peaceful park, well maintained, and clean. Let's keep it that way!