Natural
The geographic feature that forms the border between Arizona and California is the Colorado River. This river flows southwest from the Rocky Mountains and serves as a natural boundary between the two states for much of its length. Additionally, the border is marked by various reservoirs and lakes created by damming the river, such as Lake Mead and Lake Havasu.
The Colorado river
Most likely it is the Gila (hee-ya) river
Grand Canyon, in Arizona
The Colorado River forms the west boundary of Arizona with California and Nevada.
The Chesapeake Bay.
The Sierra Nevada
The border between Mexico and Texas is the Rio Grande River, also known as the Rio Bravo. The border between Arizona and the Mexican state of Baja California is the Colorado River (Rio Colorado), which also flows through the Grand Canyon and the Hoover Dam. The rest of the border between the United States of America and Mexico is made up of arbitrary straight lines, not corresponding to any natural feature.
The California-Arizona border is approximately 373 miles (600 kilometers) long. It runs along the southern edge of California, separating it from Arizona. This border includes diverse landscapes, including deserts and mountains, and is defined by both natural features and established surveys.
You can see saguaro cacti in their natural habitat in the Sonoran Desert, which spans parts of Arizona, California, and Mexico.
The Gulf of Mexico is a natural feature, located between the United States, Mexico and the island of Cuba.