If you're looking for a hike of about 10 miles in the Rancho Sierra Vista/Boney Mountain Wilderness area, consider the Old Boney Trail loop from Newbury Park. You can park either in the National Park Service parking lot or at Wendy Drive where it meets Potrero Road.
You can do the hike clockwise or counter-clockwise since it is a loop course. I prefer clockwise, which starts by trekking through Rancho Sierra Vista to Danielson Road. Details of this path are at THIS LINK. This path gets you to a juncture where you can continue another 3/10ths of a mile to the Danielson Monument (which you definitely should do if you've never been there) or veer a sharp right up the Old Boney Trail.
I love the Old Boney Trail. It is narrow and covered with growth on both sides. Kind of like running through a chaparral jungle. This makes the trail mostly shade covered for the first couple miles of this 3.5 mile stretch of trail. You'll be treated to some nice views of Boney Mountain along the way.
Although the Old Boney Trail does not reach a peak for panoramic views, you'll still find several spots that reward you with views towards the Channel Islands and west Ventura County.
About a mile or mile and a half into Old Boney Trail from Danielson Road, you'll see a turnoff sign to the right that takes you to the Fossil Trail, a mile or so drop back down to the bottom of Sycamore Canyon. The drop is about 1300 ft to 500 ft with plenty of rocky surfaces, so you'll have some fun going back down this way, for a shorter route. And of course, look closely and you'll be treated to surfaces covered with sea fossil imprints from millions of years ago.
From the Old Boney Trail/Fossil Trail juncture, you have another 2.1 fun miles to the next juncture at Blue Canyon Trail at the bottom of the canyon. You'll get some more neat views of Boney Mountain during this stretch. At the juncture is the following sign on Blue Canyon Trail.
You will turn right on Blue Canyon Trail, which will take you to the Danielson Multi-Use area and the paved Sycamore Canyon Fire Road. A left-hand turn will get you lots of fun for another day, onward to Chamberlain Trail that gets you up to some might nice peaks, and Serrano Valley.
So you run through the Danielson area to the main paved road to the right (turning left of course will take you to PCH in about 4-5 miles). In another 3 miles you'll be back in civilization; these miles include the 800 foot, 3/4 mile ascent into Rancho Sierra Vista, which can be a bit brutal...perhaps my (and maybe your) least favorite section of this course. But once you're up the hill, you're home free! Time for breakfast, lunch, dinner or all of the above!
Of course, you can easily reverse this course and make your way DOWN Sycamore Canyon Fire Road, turn left onto Blue Canyon Trail, left on Old Boney Trail for 3.5 miles and then left on Danielson Road, back down into the canyon and up towards Satwiwa.