War on weeds at Edgewood Park

"The plants tell you where the rocks are. Once you find the big ones, you can find the smaller plants," Heiple said. "In Edgewood, there are different types of plants growing on chunks of stuff, different kinds of rock."

He describes the region as a geological mess. Squeezed between the Oceanic Crust and North American Plate, the earth was pushed down quickly and brought up fast, relatively speaking in geological terms that took millions of years.

"Franciscan rock are a mess. It's like putting stuff in a blender, taking it out and throwing it out on the land," Heiple said. "It's like pudding and un-mappable."

That partly explains the unique diversity found in Edgewood Park, on the western edge of Redwood City. It is home to the diminutive Marin Dwarf Flax which occurs in the world only between Tiburon and Woodside. Its height is no taller than a pencil and its flower no larger than an eraser.

"We're lucky to have places like Edgewood. If it wasn't here, you wouldn't find this plant," said Ken Himes, a member of the California Native Plant Society.

The plant is considered a threatened species under the Endangered Species Act. For years, a group of volunteers known as Friends of Edgewood Park - along with the CNPS and the San Mateo County Parks and Recreation Department are working to restore native plant habitat. The appearance of the native flax in recent times has been one of many signs that their restoration work is turning a corner.

"But the rains have renewed their perennial concern that there are too many weeds and not enough workers. It's been a banner year for weeds and accumulating thatch prevents native plants from germinating," said a volunteer.

As Himes and Heiple work, they dream and strategize in a sea of drying wild oats, false purple brome and Italian rye, all non-native grasses. But their current campaign is against yellow star thistle, a well-armored exotic with sharp spines that cause severe wounds in horses' mouths. The group picks their battles according to a set of criteria: abundance, dispersion and invasiveness.

The group of 10 to 12 weed warriors timed their assault when the thistles are just starting to bloom. If they're too early, the plant produces more flowers. If they're too late, the seeds get dispersed. In an ideal situation, county employees would come in and mow as they have done in the past. They would follow it up with hand pulling for two or three years, said longtime volunteer John Allen. He has wrested weeds from the land since 1990 but Bob Young, another volunteer, has probably been at it since 1988.

When Allen and Young first started, their major campaign was the common teasel that threatened to take over the park in one continuous colony. The plant stands 6 feet tall and takes two years to grow from seed to maturity.

"There are no adult teasel in Edgewood. We still dig up the basal plants because there's a lot of seed in the ground," Allen said. "We can see we're making progress."

The volunteers meet twice a week in the summer time and will work through all kinds of weather except slanting rain. They see the progression of the seasons as they proceed methodically through each campaign. By turn, they hand pull or dig teasel, Italian thistle, yellow star thistle, Scotch broom and other invasive species, depending on the stage of the plant. They observe deer, quail, hawks, rabbits and are careful about ticks, rattlesnakes and poison oak.

"The group has got a feeling about the site," Allen said. "We get to go off the trail and see things others wouldn't see. There are more than 400 plant species in Edgewood. Not bad for a park that is less than one square mile."