Yesterday we took a break from learning about dinosaurs, which has been the focus of everything for the past week! We went for a hike at Nisene Marks State Park in Aptos and found our way down to a creek where almost every rock had fossils of shells in them! Back to talking all about dinosaurs and how fossils are formed, found, etc! It was awesome! 
It's SO fun to enjoy their thirst for knowledge! It's contagious! I wish we could have convinced you to part with those dinos, but he's about ready to move on to another subject already, so don't feel bad!
So sweet! This brings back so many memories.
My son studied dinosaurs passionately from about age 3 to 12. I learned waaay more about dinosaurs than I ever meant to, lol! He even went on a dig with his dad in Montana!
One afternoon he and his brother dashed into the house, exuberantly chattering about a Cooper's hawk they'd seen perched on the fence. From that day forward, it was birds, birds, birds. The dinos were left in the dust. Now I know more about birds than I ever meant to!
He has a fabulous collection of dinosaur books that he might be offering for sale soon. He once swore he'd never part with them, but now he's building a computer and needs the space. He also has a set of realistic toy dinosaurs and habitat that he's selling on Craig's List. They're indestructible, and he enjoyed them for hours. Let me know if you're interested!
Blessings!
The Pacific Plate (and another minor Plate called the Farallon Plate) is subducting (slipping under) the North American Plate along the California coast (elsewhere too but let's focus on home). This raises previously-submerged land, and the river cuts into it revealing the fossil stones. The river also transports stones from well upstream so you find a mixture of wetland and deeper-water fossils.
I have just exhausted my geo- and anthropological knowledge…