When I was a kid skiing in Norway, all hotels would have a boot brush at the front door. They didn't want you to track the snow from the great outdoors all through the foyer.
I was a bit surprised to see such boot brushes at the parking lot in Los Tranchos, one of the many beautiful hiking areas on the San Francisco Peninsula. Snow? Here? Nah...
The mats in my car often bear the evidence that I have been hiking. Gravel left and right. But a boot brush for keeping hikers' cars clean? That is a level of service I had a hard time imagining.
The brushes are not there for the cleanliness of my car mats. They are standing at trail entrances because the area suffers from Sudden Oak Death. By brushing off your boots when you leave, you can help limit the spread of the spores from the fungus that infests the trees.
This is no trivial matter - as you can see by following the link above. Throughout the eastern part of the state, the hills are full of the skeletons of former majestic oaks. That some trails are closed is a minor inconvenience compared to the tragedy of so many oaks dying around us.
As my friend - the all knowing biologist - and I were walking on one of the not-closed trails, we heard the familiar "crack-wush-boom" of a branch falling at the other side of the creek. That is nature doing its thing. But when nature does this with an oak tree, a ton of plant material may come down at once. You really want that to happen at the other side of the creek from where you are.
A mutual acquaintance was out jogging when an oak branch fell on him. With several broken ribs and vertebrae, concussion, and destroyed pieces inside, he had to stop working. But he was lucky: falling branches kill hikers and bikers in these random accidents.
So don't just look not down at the flowers and bubbling brooks but also up at what is above you. And, please, wipe your feet.