Seasonal pond at the Rock Disk Park in Marana

 

Seasonal pond at the Rock Disk Park in Marana

View towards Sombrero Peak

On the first day of 2013, I visited the Rock Disk Park in Marana. It's basically a wilderness area along the Santa Cruz River that serves as a catch basin for the rare, but powerful floods of the Santa Cruz River. The water that filled the temporary pond and irrigated the lush growth of the flood plain was mainly monsoon rain water but it also flushes the nitrogen and phosphate rich sediment from the river bottom that accumulated year-round when the river contained exclusively reclaimed water from the Roger Rd treatment facility.

Native desert vegetation does not compete well under these conditions, so the grounds are mainly covered with non-native grasses, Cockleburrs (Xanthium sp.) and Docks or Sorrel (Rumex sp). These grow in lush green carpets even in December. The corridor along the river contains several species of Salt Ceder (Eurasian Tamarix) and willows. Huge trunks of dead Cotton Wood trees are all that's left from times when the river was providing year round reliable irrigation.
  

View towards the Tortollitas

The Portland Cement factory blocks the river-path on the NW side

Greater Yellowlegs, Tringa melanoleuca and Black-necked Stilts, Himanotopus mexicanus

Nevertheless, the temporary pond with a muddy, fecund bottom attracts wintering waders and usually also dabbling ducks, but the latter were missing this year. Egrets and Herons fly over from the river that has a small population of  tiny fish, but they never stay long.

Great Egret, Ardea alba, and Black-necked Stilts, Himanotopus mexicanus

Cooper's Hawk, Accipiter cooperi

Juvenile Rufous-morph Red-tailed Hawk, Buteo jamaicensis

Great Horned Owl, Bubo virginianus

It's a great place to observe raptors. In addition to the local Red-tail, Harris and Cooper's Hawk, Harrier and owl populations, there must be many wintering birds, because there were Buteos perched in dead trees at regular intervals of less than 50 meters and several more were circling above.
 

Black Phoebe, Sayornis nigricans

Say's Phoebe, Sayornis saya

Year-old Vermillion Flycatcher, Pyrocephalus rubinus

Adult male Vermillion Flycatcher, Pyrocephalus rubinus

Flycatchers also occur in abundance. Black phoebe and whole families of Vermillions compete for perches in and around the pond, while Say's Phoebes occupy dry cockleburr stalks in the drier areas. Just around sunset several Swallows appeared swooping up insects over the water.