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A B

FIGURE 19.4 (A) Rock bedding on a grand scale in the Grand Canyon. (B) A closer example of rock bedding can be seen in this roadcut.

Younger
strata
(originally
on top)

Older strata (originally on bottom)
FIGURE 19.5 These folded rock layers are in the Calico Hills,
California. Can you figure out what might have happened to flat FIGURE 19.6 An anticline, or arching fold, in layered
rock layers to make folds like this? sediments. Note that the oldest strata are at the center.

great compressional stress must have been involved over a wide
region to wrinkle the land like this.
Anticlines, synclines, and other types of folds are not
always visible as such on Earth’s surface. The ridges of anticlines
are constantly being weathered into sediments. The sediments,
in turn, tend to collect in the troughs of synclines, filling them
in. The Appalachian Mountains have ridges of rocks that are
Younger
more resistant to weathering, forming hills and mountains. The
strata
San Joaquin Valley, on the other hand, is a very large syncline
in California.
Note that any kind of rock can be folded. Sedimentary Older
rocks are usually the best example of folding, however, since the strata
fold structures of rock layers are easy to see and describe. Fold-
ing is much harder to see in igneous or metamorphic rocks that
are blends of minerals without a layered structure. FIGURE 19.7 A syncline, showing the reverse age pattern.

19-5 CHAPTER 19 Building Earth’s Surface 481