The project garnered broad support from organizations such as the Sierra Club along with the governments of the many cities the rivers pass through. They are connected by a narrow strip in Irwindale and by Whittier Narrows to give them the appearance of a necklace if viewed from above. The goal of this program is to create a "necklace" of parks and reclaimed wild spaces with the two rivers. The Rio Hondo and San Gabriel River have both been part of a revitalization program called the Emerald Necklace. During major storms, the outlet works at Whittier Narrows Dam can direct water to either channel, or runoff can be stored. Here, both rivers are impounded by the Whittier Narrows Dam, which the Army Corps of Engineers describes as, "the central element of the Los Angeles County Drainage Area (LACDA) flood control system". Both rivers pass through the Whittier Narrows, a natural gap in the hills which form the southern boundary of the San Gabriel Valley.
For much of its length, the rivers flow parallel to each other about two miles (3 km) apart. The Rio Hondo has sometimes been described as a second channel of the San Gabriel River. Above Irwindale its main stem is known as Santa Anita Creek, which extends another 10 miles (16 km) northwards into the San Gabriel Mountains where the source, or headwaters, of the river are found.
As a named river, it begins in Irwindale and flows southwest to its confluence in South Gate, passing through several cities (though not the city of Los Angeles). The Rio Hondo (Spanish translation: "Deep River") is a tributary of the Los Angeles River in Los Angeles County, California, approximately 16.4 miles (26.4 km) long.