Dogs on leash are allowed at this wildlife reserve. It is a popular spot for birdwatching and walking. There is a minimal fee for day use. This reserve is part of the Santa Ana River Regional Park. To get there from the 91 Fwy, go east to the city of Riverside. Exit on La Sierra Ave. and turn left (north). La Sierra dead-ends into Arlington. Bear left at the signal. Drive past the hills until you come to the sign that says ”Hidden Valley.” Take the first dirt road to the right.