Obviously, the riparian area is all along the river. The trees highlighted below are ones that have been observed along the valley according to inaturalist.org. It is not a comprehensive list.
Arroyo Willow is an abundant native tree. It spreads by root runners and will tend to fill in moist areas. The flower is a yellowish catkin that is important to many insects and birds. Photo 16056750, (c) Tom Turner, some rights reserved (CC BY-NC)
The Black Willow is an important wildlife tree. It is deciduous. It can grow up to 40 feet. Flowers bloom in the early spring.
Photo from bonnienickel on iNaturalist.org taken near Poggi Creek
Broom baccharis is a flowering shrub. It grows up to 12 feet tall. It flowers abundantly in the summer, often completely covered with white or cream covered puffy flowers. Photo from brolland on iNaturalist.org taken near Wiley Road.
California Blackberry is a species in the Rose family that is native to a big part of western North America from Baja to Canada. It has prickly branches, white flowers and edible fruits. The sweet-tart fruits are dark purple to black. They can be eaten raw, baked in pie or cobbler, or frozen. Birds and butterflies love the fruits and flowers. Photo from jeffreyrmartin on iNaturalist.org.
The Coast Live Oak is a beautiful evergreen oak. Some specimens live for over 250 years! The leaves are dark green, oval, often convex; the leaf margin is spiny-toothed, with sharp thistly fibers. The outer layers of leaves are designed for maximum solar absorption. The fruit is a reddish brown acorn. They will attract a variety of birds and butterflies. Photo from hikingsandiego on iNaturalist.org.
Sometimes called Arrowweed, it was once used medicinally by Native Americans as an antidiarrheal and eyewash. Other traditional uses include thatching, arrowmaking and food, especially the edible root. Photo 25501386, (c) pj91977, all rights reserved
Desert Wild Grape is a native vine that tends to climb over other plants with stems reaching up to 50 ft. It produces edible fruits which attract many birds. Photo 23666186, (c) nateactual, all rights reserved
The Mexican elderberry is a deciduous tree with yellow flowers from April to August. Purple berries show up in September and October. Its berries are excellent in jelly. Look carefully as you pass an Elderberry you may see a hummingbird, butterfly, Jay, Thrasher, or other bird as it is an excellent wildlife plant. Personal photo.
It is usually near willows and mulefat. It has been used as a treatment for arthritis and bronchitis. It has also been used as an insect repellent. Native Americans used the wool from the leaves to cauterize wounds and treatment for poison oak. The Kumeyaay used the tea from the leaves as a decongestant. Photo 5232, (c) stonebird, some rights reserved (CC BY-SA)
Mulefat is also called seepwillow or water-wally. This is a large bush with sticky leaves and branches which bear small, fuzzy flowers. The long pointed leaves are slightly toothed. Personal photo.
All parts (roots, leaves, bark, fruits) have been used to treat a variety of ailments such as bronchitis, gingivitis, gonorrhea, warts, venereal diseases, antidepressants, toothaces, rheumatism, diarhea. For foods, the berries are used as a pepper substitute and fermented as a drink called "pulque." The wood is also used for firewood and charcoal. It has also been used as timber. The pepper tree is ubiquitous throughout the region.
It is one of the most common riparian trees in California. It is extremely fast-growing. Some reach a height of 50 feet. The bark sometimes turns reddish with age. Yellow flowers grow in drooping catkins. Birds, butterflies, caterpillars and bees love this tree.
This willow tree reaches a height of about 23 feet. It has a white fuzz around the leaves and branches. Loved by birds, bees, butterflies and moths. Photo by Kdean on iNaturalist.org.
This plant is part of the daisy family. It can reach up to 12 feet high. Important to butterflies and caterpillars. Photo 34028630, (c) Mark Dorriesfield, some rights reserved (CC BY-NC)
The genus name, Juncus, means “to join or bind” because the stems and leaves were used for weaving or binding.
It is also known as the Fremont Cottonwood and is a native to the Otay river. It can reach a height of over 100 feet. Older cottonwoods have a whitish, cracked bark. The fruit looks like cotton hanging from leaves, which is how it got its name. The leaves are heart-shaped. It's an important tree for birds and butterflies. Photo: Karen257 on iNaturalist.org
This is also called the California sycamore, California plane, and Aliso. This attractive tree grows to over 100 feet tall. The trunk usually breaks into two or more large trunks which continue to branch off. The bark is beautiful, with areas of white, gray and light brown. The bark peels away as it gets older. The leaves can get very big. The plant is deciduous, with leaves yellow and orange and brown in the fall. Personal photo.