I spent about 10 years living in San Diego Ca and spent most every winter in this great desert. Jeeping, hiking, exploring. What a great place. Since living in Arizona I have strived to return here at least once a year. This trip I had an overnighter up Rockhouse Canyon north in the park to the Rockhouses and to explore the large valley headed by Toro peak in the Santa Rosas. Phenomenal varied hiking, narrow canyon, broad valley, wash routes, cross country, big view campsite.
Next, I decamped to the southern end of the park to rehike an oldy but a goody, Mortero Palms, over the crest of the Jacumba mtns, to Goat Canyon to view the Carrizo Gorge railroad trestle. This rail line was put in the early 1900's, the trestle constructed later due to a tunnel collapse. The large trestle spanning goat canyon is supposedly the largest curved wooden railroad trestle in the world, over 600 feet long and almost 200 feet high. Way back when I used to hike the tracks to the trestle,the best dayhike I have ever done IMO. You contour about 1500-2000 feet above the Carrizo gorge, see interesting railroad remains, amazing tunnel and trestle construction. The hike is now illegal ( and was then although the railline was not in use) as local freight trains are now being run through there occasionally. This hike is the "legal" way to see the trestle. Mortero Palms is very nice, about 100 palms in a wild huge bouldered setting. This end of the park is near the oldest occupied area of the park, a boulder outcropping with alcoves has shown use by archaeologists some 5000 years ago.
Anyway, this dayhike is short but tough with a fair amount of up and down, some really steep down-climbing and rock hopping and bouldering in Goat canyon. You'll want sticky shoes on the water slicked granite. I had an unpleasant cholla encounter that I'll survive. Great New Years and a great desert.