Here in Tucson, Velvet Ash (Fraxinus velutina) trees are common in large, sandy washes with underground water and along streams in rocky canyons. These riparian trees only grow in locations where they can get a regular supply of moisture.
Velvet Ash trees are recognized by their distinctive seeds, commonly known as samaras, which are shaped like canoe paddles and by their pinnately-compound leaves with 5 to 9 lance-shaped leaflets. Velvet Ash gets its common name from the young leaves which feel somewhat velvety.
I took the photograph below of a huge Velvet Ash tree in April, and minutes later, despite the fact that the sun was still shining, the low, black clouds overhead started pelting me with big, fat raindrops. I had to stuff my camera under my shirt and run like mad through a deep, sandy wash for my car. Luckily my camera was okay and it only got slightly damp. I now always carry my water-resistant camera bag with me when exploring around during unstable weather.