Suggestions for a 3-4 day backpacking trip in SoCal?

For Southern California folk, the ranges along the coast and surrounding LA provide some hiking activity until mid June when it gets too hot.  Then there is a migration to the north to the Sierra. By May most of the snow is gone from Mt Baldy (north from I-210 on Mountain Ave) San Gorgonio out of Redlands, Mt San Jacinto before the desert on I-10.  There is water on all, but long 2+ trail days are few.  The PCT trots along or near them all.  There are good trail books of the San Gabriel as well as a wealth of trail info on individual blogs such as tchester.org/sgm/hikes.html.

For my family, Father's Day was the traditional opening of OUR backpacking season.  It was always up to Cottonwood Lakes for two or three days with young kids. The southern Sierra are generally open around mid June with a snow level near 11,000'. This means that most longer trips would mean perhaps some steep snow near the passes. On the Eastern Sierra - which generally are a shorter drive from San Diego - are:

Lone Pine: Cottonwood Lakes from Horseshoe Meadows. Trail head at 10,000+ via 26mile road from center of Lone Pine. 6 miles to lakes. There is a pleasant loop if you get over New Army pass following the PCT south to Cottonwood Pass to car. Kennedy Meadows and Whitney Meadows might be a bit wet end of May but a trip south out of Horseshoe is nice.

Independence: road west dead ends at Onion Valley. Better trip in mid to late July over Kearsarge and follow PCD/JMT south or north. Could exit out New Army Pass 5 days later (with car shuttle or lucky thumb).

Shepherd Pass trailhead just south on dirt roads off of Onion Valley Road is my favorite early spring day hike up to snow line. It is a strenuous hike uphill then loss and regain 500' to Mahogany Flat and up the trail as far as you have energy for lunch. It is the route down if you go over Kearsarge and Forester Passes for a strnuous 4 day (or 6 if you go sight seeing on the High Sierra Kern Drainage).

Big Pine: Big Pine Lakes. Check out Glacier Lodge if you want a place to sleep right at the trail head. They used to serve food before the place burned down eons ago.

Go east for trailhead up 14,000+ White Mountain. Touristy long hike to top. Just takes grit and endurance. AND Bristle Cone Pine area.

Bishop has a plethura of hikes from:
South Lake toward Bishop Pass. Another favorite spring dayhike with lots of water falls and nice weather usually. Over the pass is a relatively easy walk from South Lake.

North Lake: Nice 5 day hike to South Lake (or vice versa) via beautiful Humphrey Basin and Piute Pass. Check with Parsons Camp to see if they will give you a ride (for $) to your car at the other lake.

Sabrina Lake: A lot of nice lakes
mapper.acme.com/?ll=37.17167,-118.60162&z=14&t=T

Those are a few. Each can be a series of day hikes that will take you to about the area you would make the first night's camp. Then return to the motel, clean up and get a nice evening meal and a comfy bed. The next day do another of the hikes, etc. In May, the trail heads may not be plowed, tho. The long weekend of day hikes will give you a good introduction into what the east side is.

Or car camp and day hike up to snow level and make the grand loop north up US 395 and through Yosemite, Kings Canyon, Sequoia and Mineral King Nat Parks.  Stop at off the road spots for a looksee back in history (Bodie might be closed due to snow). There is a wealth of old mining activity still evident each with a story.  Check out a book on those.  Sequoia is huge and except for a few miles of road along a bit on the west side has a bazillion trails that you can decide to check out - over a life time.  It is definitely a back packers Park.

You might consider the California Riding & Hiking Trail in Joshua Tree. You can cache water at Covington, Ryan, Keys View Rd and/or Belle.

You need a wilderness pass anytime you spend a night in a wilderness or National Park. This allows you access to that area opened up by that trail head. Some trail heads are more controlled than others. Shepherd Pass trail has a very low quota. The trail to Mt Whitney has a large quota and a bazillion requests. You can get passes from the controlling agency for that area.

There are (or at least were) Bear proof boxes along many trails in the Sierra. You may wish to plan your hikes around those locations. They will be popular places as you can imagine. climber.org/data/BearBoxes/map.html

In most cases in the Sierra you will need to carry a personal bear resistant and approved canister. You can rent these where you get your wilderness permit. They are small. There are more expensive alternatives such as the Bearikade. There are some places that have been over camped and have been retired for our lifetime. You will find other camping regulations that include distancing your camp from water. This makes it good to have a collapsible several gallon container so you only need to make one trip to the source. It is recommended to treat or pump drinking water sources. Don't play tag with wild animals and don't make open fires. Hence the discussion on best type of stove. I like the Pocket Rocket and a 1 liter lidded pot to boil water in. On longer trips I use a MRS Dragonfly. I use a cup and a spoon for eating. A small Gerber knife to do things a small knife is good for. A head lamp has too many options for use to leave it behind.

That pretty much sums up the restrictions.

On most Sierra trails, if you are farily fit, you can probably expect a 10 mile day that will get you into camp early evening or mid afternoon. I like to have a cooked lunch with a break that is required to prepare it. If you are up and on the trail by 7AM you will be able to cover 6 miles by lunch and 4 more before you call it quits.  If you have the energy you can push a mile or so more.  If not, camp when you get tired.  It is surprisingly HOT in August at 11,000'.  Early starts are good for your body.  Almost impossible for most people to drink too much water and a trip less than a week long.

Be aware of the altitude and if you start to feel very bad (vomit, headache, no sleep), time to head down hill 1000'. It is dangerous to try to tough it out.  It is difficult to be fully acclimated, but the body adapts marvelously in most cases.

There are a lot of very high places in the Sierra. Plan not to be near or on the top of any of them during a storm. Best to plan your day so you are on your way down shortly after noon. Do not default to be a crispy critter that glows for an instant. Slight chance it will happen but...you might live through it with severe injuries.

The Sierra are generally benign. The skeeters are not. I use 100% DEET from REI. Used sparingly it lasts and lasts. It is high altitude so plan on high SPF UV protection (50+) reapplied often. Don't be one of those that peels for a week. Lip protection sunglasses and wide brim hat fits out that part of you. I carry a 200 Polarguard (or equivalent)sweater and a Precip hooded light weight jacket - for summer use. I slip my sweater on when we stop - especially on top of passes.  I keep a down vest (Columbia) in its stuff sack in bottom of pack. 20F sleeping bag on top of a 3/4 Thermarest. I bought a Stephensons Warmlite 2R years ago and have never looked back. It weighs 2.5 pounds and packs into the size of a two wine bottles cork to punt. Holds two luxuriously and 5 one rainy cold windy night.  You don't always need a tent (mainly for bugs and blowing snow).  A tarp will work in most cases.  Sometimes finicky setting up and keeping it up. 

I keep a map of the popular areas I go to on the back of a door at home.  I trace the trail when I get back and give it a date.  I carry a small USB digital recorder to keep track of my thoughts and scenic views.  I use Acme Maps (yep, same one that Wiley Coyote uses) for on line browsing (e.g., Cottonwood Lakes - mapper.acme.com/?ll=36.47203,-118.18113&z=13&t=T) [ you will need to copy and past those links].   For the Sierra, Tom Harrison Maps (.com) for planning.

Sierra South is a good Sierra reference.  As are trip reports here and other places on the net.  Learn the trees and a few brushes and berries and as many flowers as you can conveniently remember.