Hiking, biking, and horseback riding is great exercise, but it's not always just a "walk in the park." Southern California deserts are harsh environments and even experienced hikers should take care of themselves when on the trail. Carry and drink plenty of water (a minimum of 1 quart every 2 hours)
Have a plan.
Inform someone of where you're going and when you plan to return
Keep a flashlight and whistle with you
Eat well, stay hydrated: Carry plenty of water
Stay on the trail
Ask for HELP!
Familiarize yourself with the area, use a map
Expect changes in the weather
Sturdy footwear with good traction might save an ankle
Minor/moderate health or medical issues can be easily exacerbated by hiking up steep trails or hiking in high temperatures-- know your limits and pay attention to how you're feeling.
Stay on established trails.
Start with a fully charged cell phone, and bring a back-up charger.
When hiking in a group, each person should carry some water and food in case the party becomes separated, and the group should make a plan for where to meet up (at a vehicle, at the trailhead, etc.) if the members become separated.