Side Trips from Interstate 5: The Deep San Joaquin Valley
My previous side trips from I-5 have involved rocks, but that's not all there is to geology. This suggested route, an alternative to taking I-5 straight south to Los Angeles, will expose you to the southern Great Valley's hydrology and many excellent, recently excavated fossils.
Start by exiting at Santa Nella — not to patronize the garish set of businesses there, but to take state route 152 east. You'll go all the way across the valley to Route 99, then south from there to the "Grapevine".
The first thing you'll notice, if you haven't already, is the profusion of canals in the Valley. They come in all sizes, ranging from the Edmund G. Brown Aqueduct (that's the first one you cross) down to uncountable numbers of field ditches. There are natural streams, but most of the water you'll see is in canals. This one runs parallel to the San Joaquin River about 6 miles west of Dos Palos Y.
Right next to it, the river that gave its name to the San Joaquin Valley was a sandy ditch in March during the rainy season. In good weather you'll be able to see mountains wherever you are, either the Coast Range on the west or the Sierra Nevada on the east (as seen here). I believe that there is no place in California where mountains are not visible if the air is clear.
The far end of route 152 meets Route 99. I recommend the old-timey charm of Chowchilla just north of here for a road stop, but otherwise you'll turn south on 99 and take the very first exit to the Fossil Discovery Center of Madera County.
The center is across the road from a sanitary landfill, and for a good reason: in 1996, diggers at the new Fairmead landfill uncovered a complete mammoth tusk. Soon it was realized that the site contained a world-class Irvingtonian fossil fauna dating from the mid-Pleistocene about half a million years ago. (There's a Bay Area connection here: the Irvingtonian is named for the wonderful bone beds unearthed in the East Bay's Irvington district during freeway construction in the 1940s.)
A paleontological foundation was set up and scientific ties established at nearby Cal State Fresno. Whenever the landfill operators open up a new pit, fossil scientists are on hand to harvest what they can. Bones of mammoths, wolves, sabertooth cats, horses, camels, ground sloths and many smaller creatures are stockpiled and studied at leisure between digs. The Fossil Discovery Center opened its doors in late 2010 and makes an excellent visit whatever your level of interest or expertise. Its outdoor "Pleistocene Water Source" exhibit makes it easy to imagine the lush scene in ancient times.
You can sit out back, next to the fossil washing station, and cast your eye over the surrounding land. I was told that the center has options on some of this acreage, where thousands more fossils surely lie in wait.
Eventually you'll need to return to 99 and resume your journey. Another stop you should consider is in Bakersfield, where less than 5 miles east of the road on Stockdale Highway is the city's gracious new Riverwalk Park on the Kern River, which is still a vigorous stream here.