What is the Base and Meridian Wildlife Area?
Thirty miles downstream of Scottsdale the Salt River, which has been a dry wash through most of the city, comes back to life on the outflow of the 91st Avenue treatment plant and runs green and wide through cottonwoods to meet the Gila below Avondale. On the north bank at that confluence, where Avondale Boulevard (the old 115th Avenue) once forded the river, the Arizona Game and Fish Department manages about 198 acres of marsh, open water and riparian forest as the Base and Meridian Wildlife Area. The department runs it for waterfowl and for the two federally listed birds that live here, the Yuma Ridgway’s rail in the cattails and the western yellow-billed cuckoo in the cottonwoods, and the site sits inside a globally recognized Important Bird Area for the rail and the Neotropic cormorant.
For visitors that means a gravel lot, a flat dirt path along the river, a kayak launch, fishing holes and no interpretive anything; it rewards binoculars and patience. One weekend each March the city of Avondale sets up the Tres Rios Nature Festival here, with free canoeing, archery and bird walks. The name is a surveying fact, not a brand. The Gila and Salt River Meridian and its Base Line cross at an initial point set in 1865 on the small hill just south of the river, and every township, range and section in Arizona is measured from it; Phoenix’s Baseline Road runs along the same line.
What you get is sixty bird species before breakfast, a free lot and a flat walk 45 minutes from Old Town, beside the hill where Arizona’s map begins. What you do not get is a restroom, a sign, shade in summer, or any wilderness: it is a managed marsh fed by a treatment plant, with a racetrack across the river. The birds do not care, and in January neither will you.
How to visit Base and Meridian right
Pay nothing, but know whose land you are on. No pass, no permit, no fee. The Tres Rios wetlands to the east, built by the City of Phoenix around the treatment plant outflow, are a separate property with their own free entry pass and gate, and visitors routinely confuse the two; plan that visit separately. A state fishing license is required to fish.
Get there. Loop 101 south to I-10 west, exit Avondale Boulevard and go south about six miles through Avondale, past the Phoenix Raceway, until the road drops to the river. The wildlife area lot is on the right before the crossing, at the 7602 S. Avondale Blvd. address. Figure 45 minutes from Old Town with no traffic; on a NASCAR weekend the road is a parking lot. The lot is gravel and the trail is dirt.
Go at first light, in winter. November through March is the season for ducks and comfortable walking; April and May bring migrants and singing rails. Walk east along the north bank from the lot. The cattail margins hold rails you will hear long before you see them, and the big cottonwoods on the Salt side are where the herons and night herons roost. Summer is hot and thick with mosquitoes.
Bring boots and binoculars. No water, no restrooms outside festival weekend, no shade to speak of. The trail is dirt and the low crossing floods; after any rain, wear rubber boots. The wildlife field guide covers what else uses the river corridor, from beavers to bobcats.
Do not drive the crossing. Do not take a vehicle down the old low-water crossing of the Gila even if you see tire tracks; it is the kind of place the stupid motorist law was written for, and the paving rebuilt in 2025 does not change that when the river is up. Game and Fish closes the whole area when it floods; check the department’s site or Avondale’s updates after a storm.
Paddle if you like. The kayak launch puts you on the Gila below the confluence; the current is slow and the cottonwood banks are the best view of the place. Launch early and take the water seriously after storms.
Dogs. Allowed on leash on a Game and Fish wildlife area, but this is nesting habitat for an endangered rail and a poor place to let one run.
Pick the festival weekend with kids, avoid it otherwise. The Tres Rios Nature Festival in March is the one weekend the place is crowded, with free canoeing, archery and bird walks, and it is worth it with children.
Skip it if you want desert mountains. Estrella Mountain Regional Park is 15 minutes west with trails, restrooms and a view back over the confluence; for the Salt’s other engineered end, Granite Reef Dam upstream of Scottsdale is where the river’s water is taken out, and this is where what remains comes back.
The hill where the map begins, and the river that came back
The confluence was farmland two thousand years before it was a wildlife area. The Hohokam dug canals on both the Salt and the Gila and farmed the plain where the two rivers meet, and their descendants, the Akimel O’odham and Piipaash, still hold the Gila a few miles upstream as the Gila River Indian Community. The 150-foot hill on the south bank that everything else in this story turns on was, to them, simply the one place on the plain you could see the whole river from.
That is why the surveyors picked it. In 1851, as the United States and Mexico surveyed the new boundary drawn by the Treaty of Guadalupe Hidalgo, a boundary party raised an eight-foot rock monument on the summit of what became Monument Hill as a reference point, visible from everywhere on the plain and set beside the biggest landmark in the region, the meeting of the two rivers. The border moved south with the Gadsden Purchase three years later, but the monument stayed. When the Surveyor General began laying out the Territory of Arizona for sale and settlement, he adopted the existing point: in 1865 it became the initial point of the Gila and Salt River Meridian and Base Line, and in 1867 the first township surveys ran out from it. Every section, township and range in the state is counted from this hill, north and south of the base line and east and west of the meridian; the legal description on a Scottsdale deed, and Baseline Road across the south Valley, both begin here.
The point has needed defending. The Bureau of Land Management re-monumented it on December 1, 1944, again on April 24, 1962 after vandals wrecked the marker, and on April 26, 1984, when the BLM, the Gila River Indian Community and Arizona’s surveyors built the present monument during the first National Surveyors Week. It was listed on the National Register of Historic Places on October 15, 2002, and the concrete cross with its tile inlay was rebuilt in 2006. Across the river from it, on 320 acres against the Estrellas, Phoenix International Raceway opened on January 4, 1964, which is why a quiet wildlife area has a NASCAR weekend.
The river itself is the stranger story. For most of the twentieth century the Salt below Granite Reef Dam was dry, every drop taken for the Valley’s canals, and the Gila below Coolidge Dam not much better; the confluence was sand and tamarisk. What brought it back was sewage. Phoenix’s 91st Avenue treatment plant discharges its effluent into the Salt a few miles upstream, and from the 1990s the city and the Army Corps of Engineers turned that outflow into the Tres Rios wetlands, acres of constructed marsh that polish the water and, as a side effect, recreated the cottonwood-willow forest and cattail marsh the lower Salt had lost. The water flowing past the wildlife area today is treated wastewater, and the rails, cormorants and cuckoos that make this a globally recognized Important Bird Area are living on it. Game and Fish manages the north bank at the confluence for exactly those birds, and Avondale, which grew from a farm town to a city of 90,000 around it, stages its spring nature festival on the department’s ground.
The last chapter is maintenance. The old 115th Avenue low-water crossing of the Gila, now Avondale Boulevard, bisects the area and floods every wet winter; years of it had broken the paving and the embankments. In 2025 Avondale and Game and Fish closed the entire wildlife area from October 1 to December 31, pausing only for race week, to repave the crossing, repair the banks, regrade the staging areas and rebuild the trail to the kayak launch. The next big flood will test the work, and the area will close again when it comes.
Why it matters
Base and Meridian is the Valley’s plumbing and its paperwork in one place. The hill is where Arizona’s grid of ownership starts, the reason every lot in Scottsdale has a legal description; the river below it is where the Valley’s used water comes back to the surface and turns, against all odds, into the best marsh in the West Valley. That the state’s endangered rail now depends on Phoenix’s effluent is the kind of fact this region specializes in. For a Scottsdale visitor the verdict is plain: it is a flat, free, excellent winter birding morning 45 minutes away, not a hike and not a wilderness; go at dawn between November and March, stay out of the crossing, and look across the river at the hill the whole state is measured from.