A tall, sprawling bush grows in a rocky creek bed, decorated with cone-shaped heads of purple pea flowers. Plain, broadly pointed leaves are arranged in threes. Often the leaves are folded slightly towards their central vein, and also bent at a sharp angle to the stem so they look upraised, like a hand cocked at the wrist.
This is California hemp (Hoita macrostachya). This leggy plant has hollow stems and likes to live in moist places and is a good indicator of wetlands. It is found almost exclusively in California, as are the other two species in the Hoita tribe. All have purple flowers and similar leaves, but one is a creeping, low-growing plant and the other is found in serpentine chaparral, not in wetlands.
The name California hemp likely derives from this plants historic use as a textile. The fibers of its stem are strong enough that they reputedly have been used for sewing, as well as been woven into ropes or bags. A yellow dye can be made from its roots. 
Flowers Of Marin 