Let's face it. The human body was not built to run 30, 40, 50+ miles per week solely on pavement.
Buy the best pair of shoes, stretch, rest a lot, get massages, but you are putting your joints and ligaments at risk by pounding out all of your mileage on streets and sidewalks.
That's not to say it isn't a good idea to do some significant training on the roads. In fact, if you are training for a road race, particularly a marathon, it behooves you to train quite a bit on that surface. If you don't, your body will not be fully prepared for 26.2 miles of pounding on the roads.
But try to get out there in the trails and more "giving" surfaces as much as you can. If you live here in sunny Southern California, surrounded by mountains and beaches, you've got it made. Here in the Conejo Valley, we are surrounded by hundreds of miles of open space and trails. Some of my local favorites are Sycamore Canyon, Cheseboro Canyon and the Los Robles Trail. But there are so many to choose from.
Now for the pros and cons of trail running. The pros are: easier on the body, scenic, gets you back to nature, great for improving foot/eye coordination, gets you away from car fumes, etc. The main drawbacks are higher chance of twisting your ankle on rocks (gotta be careful!) and possible wildlife encounters. On that note, I do have a few friends that refuse to run trails because they are afraid of snakes. I agree that you need to be aware...I run trails 5 days a week and see a snake probably once every few months...mostly in the summer.
Of course on the trails you have to deal with creepy crawlies, gnats (I've run through some nasty swarms at times...usually in the late spring), bees (got stung on the back of my head once, but I survived), etc. I see coyotes all the time but they are scrawny and stay away from me, even though I am scrawnier. Of course, you also need to be aware of poison oak..."leaves of three...let it be."
But don't let those minor matters scare you away! You've gotta try it and you'll be hooked! And your body will thank you for it.
And consider running an upcoming local trail race! Great stuff. You'll meet a lot of fun people.