I mentioned my favorite hike awhile back. However the hike I linked to isn't actually mentioned (in its entirety) at the link I gave. The reason? Because, as far as I can tell, it is not mentioned at any of the hiking sites that I know about. I call it the Temescal / Will Rogers Hike. It is around 13 miles with a total elevation of about 1100 feet (most of that in the first 2 miles).
The basic path is to start from Temescal Gateway Park heading north. This is the hardest climb you will have during the hike. You get some very nice views of Santa Monica.
Eventually you will come to a fork. You can either go down to the waterfall or you can go up toward Skull Rock. Go to Skull Rock. After you pass Skull Rock you'll walk above a housing development and later on some power lines.
Eventually you will come to a dirt road and you will see this post.
Continue north along the dirt road.
You will eventually see the following sign. It will be facing the opposite way that you are walking and, at times, may be easy to miss.
Eventually you will come to a sign that says Backbone Trail at a 'T' in the road. Head east. There are some very good views of Century City and, later on, the valley.
This is the longest portion of the hike. After around 6-7 miles you will reach Will Rogers State Historic Park. Head toward the polo ground and then head west toward the bathrooms (and drinking fountains!). To the west of the bathrooms the trail continues.
At a point around 1-1.5 miles before completion of the hike you will come to a fork. You can either go up onto a hill or stay down below. Go up onto the hill. The other way is an unmaintained path. I don't know where it goes, but I did mistakenly hike on it for a few hours the first time I took this hike. Big mistake.
Probably the best hiking site for the Los Angeles area is This Hiking Trail. It's the site where I first discovered my favorite hike. I just recently discovered the trailhead to a hike very close to where I live. It's a moderate distance at 7.8 miles, but is fairly strenuous at over 2000 feet in elevation from start to highest point. The point of all this is to show the usefulness of the site. It lists several dozen area hikes, links to other hiking sites, and (actually useful) comments from other hikers.