Historical Articles of Solano County

Sunday, March 17, 1996

Prehistoric camels roamed Potrero Hills

Kristin Delaplane

First in a series
The low-range Potrero Hills start about three miles southeast of Fairfield and run some five miles or 10,000 acres. The maximum elevation is 400 feet above sea level.
The geologists find the fact that they run in an east-west direction - interesting, as the majority of such features in the area run northwest.

Looking back at the Potrero Hills from Grizzly Island Road, the round mounds that make up the hills appear as a string of giant pearls of irregular size undulating as the strand retreats into the distance.

The hills are the topographic expression of an anticlinal fold in Eocene rocks which were deposited in shallow waters some 65 million years ago.

It is surmised that the hills have been uplifted and eroded many times, beginning with the late Jurassic period and continuing into the late Pliocene, an interval of some 135 million years.

The hills assumed their present form as a result of a fairly recent late Pliocene crustal disturbance, only being somewhat modified since by erosion.

The thickness of rocks overlying the basement complex is unknown; however, exposed rock in the surrounding area suggests that up to 32,000 feet of Jurassic, 19,000 to 500,000 feet of Cretaceous and 5,000 feet of Eocene sediments have been laid down in ancient seas in the vicinity.

It is probable that some 1,200 feet of Pliocene sediments were also deposited on the Eocene rocks presently exposed and then subsequently removed by erosion. All this represents approximately 180 million years of geologic history.

Fossils of camel and horse teeth from the age of prehistoric mammals were found near Denverton.

A Pliomastodon skull was found in the Montezuma Hills that lie southeast of the Potrero Hills, and fossil mastodon teeth were found in Putah Creek. These ancient animals, which became extinct some 8,000 to 12,000 years ago, are believed to have migrated across the Aleutian Islands land bridge that existed between Asia and America.

While the Potrero Hills was not an area heavy populated by Indians, some of their stone utensils were unearthed in these hills. These artifacts show that these few Indians inhabited the area a mere 4,000 years ago.

During the time of the Indians, tule elk (wapiti) from the adjoining marshes often roamed onto the treeless Potrero Hills to feast on the wild oats that flourished there.

The elk population was quite large and many generations shed their horns on the hills. These shed horns were plainly visibly when the first pioneers arrived in the area. The last tule elk was said to have been killed in 1861. Only in recent years have these elk been reintroduced to the area, and are now thriving once again.

In the winter, the skies were filled with migrating ducks and geese. By the time the area was well-settled, this became a favorite area for sport hunting. The bird life was so great that during the season, September to March, the legal limit was as many as 50 ducks per day.

The Potrero Hills received their name from the Spanish-speaking people when they arrived in the area. Potrero means “pasture.”

None of the early Mexican land grants covered the Potrero Hills, but the early Mexican rancheros bred what would be considered today wild cattle, which grazed freely throughout both the Montezuma and Potrero Hills. These animals were known as “all hide and horns,” but they served a purpose, as they were mainly slaughtered for their hides and tallow, which brought in a good profit.

The Potrero Hills began to be somewhat settled when the lands were claimed by the Americans and more people moved into the area.

These pioneers reportedly determined the fertility of the soil by the height of the wild oats. If they grew tall enough to be grabbed and tied across the back of a horse, the ground was worth farming. The Potrero Hills weren’t considered suitable for farming, as the oats grew to only 3 feet.

But these hills did provide good pasture land for horses and cattle, so a few settlers were inclined there to raise stock. These new settlers brought with them cattle that were noted for their beefsteaks.

The marshlands adjacent to the Potrero Hills, Grizzly Island, were a valuable part of the land area, providing good forage for the stock in late summer.

Hiram Rush came across the plains in 1849 driving a herd of cattle. In 1852, he came to the Potrero Hills. In time, he owned 5,100 acres of land there.

Though its ranch was in the Potrero Hills, the family had its residence in the thriving town of Suisun City. Hiram Rush died in the Potrero Hills when his buggy capsized on one of the steep inclines.

His son Benjamin Rush continued the family ranching business. Benjamin not only was noted as the area’s leading citizens, but was also a state senator for 24 years.

In telling stories of ranching in the area, Benjamin often related his about the many narrow beaver channels that interlaced the marshland. Because his cattle were often caught in these channels, the cowboys were required to ride the tule track daily so as to rescue cattle from the hidden beaver channels, which could be 3 feet in depth.

Rush constructed a landing on the Suisun Slough for shipping wheat from the Potrero Hills. But before any farm machinery could harvest the wheat, Rush first had to see to it that the numerous elk horns were picked up.

Then the wild geese proved to be a problem during the sprouting season, since they quite enjoyed feasting on these young, tasty morsels. During this delicate growth time, shotguns were put in use starting at 4 o’clock in the morning until sunrise had broken over the hills and marshes.

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