This town has a bus stop, but virtually no bus service. You almost certainly have to travel here by private car or plane (unless you're a hardy one that can ride your bike or horse here). There is a car rental place, last time I checked, and you can probably order a cab at great expense, but forget about the bus unless you have to.
There is basically one bus that runs in this town two times a week (Thursday and Friday). It leaves in the morning and comes back in the afternoon on both these days. It is a very, very, long trip, about 3 hours. And, the cost is $10.00 each way if you need to go all the way down to the El Cajon Trolley Station. ($5.00 to and from Ramona).
A 4 wheel drive vehicle would be your best way to get around the park if you do not plan to hike, ride a bike, or go on horseback. However, a passenger car can be used to get around to certain areas of the park. But, you will actually miss out of some interesting features of the area that are only accessible via rough or sandy roads and trails. At times, many of the dirt roads are accessible to a passenger card, but at others, many are not. Check with the park's visitor's center for all road conditions. If they say you must have a 4 wheel drive, high clearance, vehicle, then don't take a passenger car.
Coyote Canyon is accessible in a car if you take it slowly on the graded dirt road. There are three water crossings through Coyote Creek that can hamper making it more than 4 miles up the canyon. Many cars can make the first shallow water crossing and then there is a parking area at the second crossing where you can park and continue up the canyon on foot.
When you drive up Coyote Canyon take care in checking out how deep the final water crossing is. It varies during the year. A 4 x 4 vehicle can get through but can stall out when the water is at higher levels.
Though the roads are for the most part not paved, the trails do have clear signage for the various washes and trails. If you have a good backcountry or park map it would be hard to get lost. Even when you know where you are, it seems like you are located somewhere on Mars and will never find your way home.
In the Arroyo Seco del Diablo there are currently 2 large landslides blocking the trail as of February 2005. Attempt going over at your own risk.