The backbone trail is a trail that runs more or less along the ridgeline from Will Rogers State Park near Sunset Blvd 70 miles up the coast through Malibu to its end in Point Mugu. You can access the backbone trail from many other trails that dot the coast from Pacific Palisades.
Will Rogers State park is a great place to start and parking costs around $7 or so. The park is open from Sunrise to Sunset. You can even bring a dog here...keep in mind that many of the other trails are not dog friendly..head south to Palos Verdes for that. The Backbone trail is not a hard trail per say...I've done different parts of it in Vans tennis shoes which are more deck or skate shoes...no hiking boots required unless you want to head up some of the harder trails. There are numerous books on the area that you can buy at Boarders or B&N plus countless internet sites where you can print maps etc. It's a great way to see the native plants, the coast, the old filming site of the "MASH" TV show which was a Korean War comedy with Alan Alda staring in it where they have a few old jeeps etc. laying around. Come up here when it has been raining and you can see some cool waterfalls that make for some good photos.....Check my other off the beaten path tips for more photos. There are some good mountain bike trials that will bloody the shins of even experienced riders. Check the net and you can also find info on horseback riding here.
If you have a car and like to hike, take PCH up into Malibu and turn right on Malibu Canyon, proceed inland about 5 miles, and park in the lot for Malibu Canyon Park. Take the Back Bone trail up to the peaks for stunning views of Santa Monica Bay and the coast of Los Angeles to Palos Verdes and Catalina Island. Usually not crowded at all, the hike is remote and fairly strenuous. I did this 3/12/06 in 3 hours at a moderate pace.