Note the architectural treatment at the ends of the piers, the vertical exterior girder, and the rather monolithic appearance of these bridges. That must be the modern, streamlined appearance of late 1960s bridge design in California.
Besides the occasional kayak, you don't see a lot of boats on the American River. Just downstream (near the confluence with the Sacramento River) the speed limit restriction is lifted, the water is much deeper, and the river is filled with jet-skis, motorboats, and big yachts.
American River Bridges: I-5 Expressway Bridges by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.