It is perhaps the most popular group of rocks in the East Bay.
Rock City on Mount Diablo draws visitors from all sides of the mountain.
In fact, park rangers say it's the second most visited site on the mountain behind only the summit itself.
There are a number of reasons for Rock City's popularity.
One is its accessibility.
The rock formations are about halfway up the mountain's southern road between Danville and the summit. There is a large parking lot and picnic tables there, too.
Rock City is also simple. Most of the formations are in a relatively small area. That makes it easy for families with younger children to explore. If your kids like to climb, this is the place for them.
"Rock City is in a nice, contained area that is convenient for families," said Mount Diablo park ranger Carl Nielson.
There is also the geologic interest.
The rocks are sedimentary sandstone rocks that are easily carved by water and wind.
Those forces of nature have created small caves and tunnels that younger children seem to really enjoy. It's also made it easy for people to carve their initials and other inscriptions into the rocks.
One of the most prominent features of Rock City is Sentinel Rock. In his book, "Mountain Lore," Rich McDrew describes this popular monument as a "large boulder made of massive sandstone."
The rock has quite a view from the top. It's a relatively easy climb thanks to the chiseled steps and the safety railings installed by the Civilian Conservation Corps in the 1930s.
Rock City is part of an uplifted rock formation known informally as Wall Point that extends up the southern side of the mountain.