Fish Creek begins 15.7 or so miles up the creek bed in Hapaha Flat in the Vallecito Mountains at an elevation of about 2,600 feet. It meanders south and then northeastward and eastward to the Salton Sea, or if would if the water wasn't absorbed into the ground before it got there.
As you walk westward uphill through the Split Mountain divide, you are walking into country guaranteed to excite geologists, and anyone else who appreciates red earth, big rock formations, and old mud with rocks stuck in it. All around you, the faces of cliffs are stuck full of rocks. The geologists, who have a name for everything out here, call this fanglomerate, a mud and rock mixture that dates back 20 million years.
Toward the top of the hill is a place where rock plates are piled on top of each other and beside each other, resembling stacks of plates in a madhouse kitchen. In one particular place is a stack of rock plates whose sides have been forced downward by the weight on the plates above them. It is called an anticline. Beside it is a pile of plates whose middles bend down. This pile is called a syncline. These formations are 23 million years old.
What you see in Split Mountain is well described in a little masterpiece of nature writing by the late Dr. Horace Parker. Parker's Anza-Borrego Desert Guide Book, first published in 1957, is now to be found only in the libraries of collectors and in second-hand bookstores. Parker wrote as follows:
"Split Mountain's height and mass forms awesome patterns, constantly drawing one's eyes upward to search for new points of interest along the canyon's walls. Geologically speaking, Mother Nature went berserk mixing a potpourri of her many arts. There are granites and lava dikes, sandstones and mudstone, marine deposits and fresh-water deposits, anticlines and synclines, hanging walls and footwalls, fault zones and landslides, with igneous, sedimentary and metamorphic rocks and combinations of each. And to top if off, she made a special plum pudding called Split Mountain fanglomerate, in which worn and rounded stones, like raisins, are embedded in a matrix of sandstone alluvium. To add a touch of humor, she liberally garnished the area with ridiculously formed sandstone concretions. Then she cut, sculptured, and tilted the entire mess into a rock-candy pattern of canyons, washes, and broad valleys."
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