Be careful of sitting on rocks when you are out hiking!
Read the article in full in the link above – but in short, the California Department of Public Health found that out of leaf litter, downed wood, tree bole (lower 5 ft of tree trunks), and rocks, the most nymphal ticks were found on rocks.
According to Dorothy Kupcha Leland, California nymphal ticks have a much higher Lyme infection rate than adult ticks, but due to the bigger size, most studies have been of adults. (Please see link above for informative graphics)
https://www.lymedisease.org/tildenticks-2/ Also, according to this 2011 article, California researchers have also found nymphs in unexpected places, including on and underneath wooden picnic tables and benches.
My personal advice is to wear permethrin-treated clothing when spending time in such a place. (At the very least, on the bottom half of your body: shoes, socks, and pants. But what the heck, how about a treated shirt and hat, too?) And wear repellent on exposed skin. And check yourself often for ticks, promptly removing any you find. https://www.lymedisease.org/lyme-basics/ticks/personal-protection/
https://madisonarealymesupportgroup.com/2017/03/10/national-pest-alert/ I posted this recently, but here it is again. This is the National Pest Alert.