Download Diorite - El Camino College

Monrovia Canyon Park is located in the foothills of the San Gabriel Mountains at an elevation of
1300 feet above sea level. It includes a riparian (creek-side) ecosystem as well as chaparral on
the more exposed slopes. The nature trail starts less than 100 meters up the road (left side) from
the cabin parking lot. Use this handout to help guide you along the nature trail.
Poison Oak (Rhus toxicodendron or Rhus diversilobum) – DON’T TOUCH!
A member of the sumac family, this is one of California’s most widespread shrubs. It is
easily recognized by its leaves growing in groups of three. In the fall, its brilliant red foliage
colors many slopes and roadsides, but it prefers shady areas. The lobed leaves, steps, and
roots of this plant contain oils which produce an irritating rash, and can be very severe on
some people. If the plant is touched, you should immediately wash with soap and cool water.
There is also a commercial product which is best for removing the oils. Made by Tecnu it is
sold at pharmacies. Poison oak is a food source for deer and was used by California Indians
for basketry and as a black dye.
Bracken Fern (Pteridium aquilinum pubescens)
This western native prefers sunny to semi-shaded areas and is somewhat drought tolerant.
It can grow up to seven feet under good conditions, but goes dormant if sufficient moisture
isn’t received to sustain foliage. The immature fiddle heads may have been used by
California Indians as an asparagus-like vegetable.
Mugwort (Artemisia douglasiana) Mugwort is a member of the sage family and was used often
by the California Indians for medicinal purposes. It was used as a tea or drink for stomach
problems. Heating mashed mugwort leaves and applying to the painful area supposedly
helped arthritis, bruises, and back pains. Probably the best known use was in treating poison
oak rash. Mugwort grows in sunny areas and during very hot weather it turns its leaves over
to reflect the sun off of the white underside.
Toyon (Heteromeles arbutifolia) (left side of trail)
This evergreen shrub (in contrast to deciduous) grows up to approximately 3,500 feet
elevation on rocky slopes, in canyon bottoms and is often planted in parks and gardens. The
small berries are usually green in early fall, but by late fall and winter they turn red and
provide food for birds. Leaves are leathery, oblong shaped and dark green, with toothed
edges. California Indians cooked the berries by roasting over hot coals or in a basket of hot
stones.
Diorite
As you walk along the trail, notice the light-colored rocks with the speckled dark minerals.
This is an igneous rock which formed when magma (molten rock) cooled off slowly and
solidified deep underground. Although confused with granite, diorite is different in having
more of the dark, mafic minerals than granite does.
Notice the effect of tree roots on this slope. The roots at one time were covered by soil, but
the erosional effect of water has exposed them. Now the roots minimize further erosion.
Notice the diorite boulders amid the roots.
The Power of Water
As you walk on the next stretch of trail, notice the level of the trail below the adjacent
ground. The winter of 1998 had twice as much rain as normal, but the erosion was 10 to 20
times greater than normal. Much of the runoff flowed down this part of the trail, washing
away much of the clay and silt, leaving the heavier sand and boulders in place. Watch your
step.
White Alder (Alnus rhombifolia) the large tree on left side with low branches above the trail
This is the only species of alder native to Southern California and is one of the most common
trees along streams here. Growing to 100 feet tall, it needs moist soil so it isn’t found on more
exposed slopes. A deciduous tree, the white alder has tiny cones growing in clusters at the end
of its twigs. Leaves are oval with fine teeth along the edges. The cones are very small in early
October, but very pronounced by Thanksgiving. Notice how the tree roots hold onto the soil
near the stream while the surrounding area has been washed away during the periods of heavy
runoff.
Quickweed (Ageratina)
A prolific grower in moist soil near streams and other water sources. Leaves are bright green,
arrowhead shaped with a toothed edge. The small flowers are white and grow in clusters at
the end of stems. Notice the white squiggly lines on the leaves. They are caused by an insect
larvae called leaf miners.
Canyon Live Oak (Quercus chrysolepis) 1st big tree on left side of trail
The Canyon Live Oak is adapted to moist canyons below 6,500 feet. The oval leaves have
smooth edges. Look for acorns with their prominent cap. The yellowish fuzz on the large
cap has led the tree to also be called the Golden Cup Oak.
Coast Live Oak (Quercus agrifolia) 2nd big tree on left side of trail
This is one of the most common oaks in southern California. It may be found in valleys and
canyons below 3,000 feet and has cup-shaped leaves with toothed edges. The acorns are
slender in comparison to those of the Canyon Live Oak. Acorns from both trees were the
most basic food for the California Indians, providing them with meal for breads and soup.
The acorns are NOT tasty if eaten raw, however!
14. California Laurel (Umbellularia californica)
Also called California Bay, this aromatic-leaved evergreen tree grows in shaded canyons
below 5,000 feet. Cream-colored flowers develop in early spring. The 3-5 inch long, glossy
leaves are very fragrant when crushed and were used by the California Indians to cure
headaches.
Big Leaf Maple (acer macrophyllum)
This tree has the largest leaves of any of the 120 species of maple trees in America. It is found in
canyons below 3,000’ so it is also called Canyon Maple. As a deciduous tree its leaves change color
before dropping. Notice the seeds; they are “winged” to aid dispersal. A seed dropped directly under
the parent tree would have less of a chance for space and sunlight; nature has equipped some seeds
with a means of travel, such as the little “wings” on the seed of this tree. The sap of the Big Leaf
maple has been said to be as good as that of the Eastern Sugar Maple. This tree can live as long as 200
years.
California Sycamore (Platanus racemosa) – next large tree on left side after maple; whitish bark
A large deciduous tree found in canyons and river bottoms, it requires large amounts of
water. Leaves are similar to the Big-Leaf Maple, but are shorter stemmed and do not get as
colorful in autumn as maple leaves. The bark of the sycamore is very different than the
maple. Sycamore bark is thin and peels off in jigsaw puzzle shaped pieces of beige and gray.
22. Laurel Sumac (Rhus laurina)
A common, evergreen shrub or small tree of the chaparral plant community. Its tough,
leathery leaves help the plant conserve water by reducing water loss during the hot summer
months. It has an extensive root system to search for important moisture. This shrub is
closely related to poison oak and has been known to irritate the skin in rare instances. A
related species is called Poison Sumac and is even more virulent than poison oak.
After the laurel sumac, continue upstream ¾ mile to Monrovia Falls.