Spanish explorers brought domestic swine to California starting in 1769 and European wild boars were introduced in 1925 for hunting. Their offspring can now be found in the wild, including in Pinnacles National Park. Unlike the peccaries found in other parts of the Americas, these European wild pigs are not native to this part of the world and are considered an invasive exotic species. The pigs have an extremely broad diet and will root around in the ground for acorns, grasses, forbs, berries, roots, bulbs, insects, and worms, but will also eat reptiles, amphibians, fish, small mammals, and carrion. Not only do they eat the food needed by native species, they consume great quantities of seeds and seedlings that would become the next generation of plants in the park. Through their foraging they churn up soil in much the way machinery would, causing tremendous damage, drying the soil, and creating opportunities for invasive plant species to move in. Wild pigs are able to survive in harsh conditions, can have two litters of 4-14 piglets each per year, and have few natural predators, making these invaders very hard to control.
Enter the fence.
Completed in 2003, the pig exclusion fence at Pinnacles encloses over 14,000 acres and stretches about 24 miles, barring pigs while allowing other wildlife to pass. In that same year, researchers from the University of North Dakota began a two-year study on the vegetation and soil conditions within the fenced area and developed methods that the park could use to continue monitoring after the pigs were gone. These researchers found that rooting had indeed caused significant damage to both soils and vegetation.
By 2006 the fenced area was deemed free of pigs and the vegetation has been recovering well since. In 2010 the park added another nine miles of fence to protect more than 2,000 additional acres of sensitive habitats including riparian and wetland areas where federally threatened California red-legged frogs breed.