One of the more spectacular natural phenomena in the Bay Area is the arrival of monarch butterflies for their annual winter stopover on what has been described as an intergenerational relay race that can traverse a thousand miles or more.

A great place to enjoy the show is Ardenwood Historic Farm in Fremont, where colorful clouds of the insects cluster together in a eucalyptus grove. They usually start arriving in November and stay until early to mid-January. This year they're orange and black in honor of the San Francisco Giants' World Series victory (actually they're always more or less those colors).

Naturalist Chris Garcia launches the first in a whole series of programs about the Ardenwood monarchs in a session from 2 to 3 p.m. Sunday. Meet Chris at the Ardenwood granary for a walk to the grove to see if any butterflies have arrived, and to learn about their life cycle.

The program is free of charge. Ardenwood Historic Farm is located at 34600 Ardenwood Blvd., just north of Highway 84 (the Dumbarton Bridge approach) in Fremont. The entrance fee Sunday will be $6 for adults, $5 for seniors and $4 for youngsters ages 4 to 17. Children three and younger get in free, and parking is free. For more information, call 888-327-2757, ext. 2797.

WALK THAT DOG: Over at Sunol Regional Wilderness there still may be time to register for a "Canine Caper" walk with your favorite four-legged friend up to the top of Mission Peak.

This is a steep, strenuous hike from 9 a.m. to 3 p.m. Saturday, led by naturalist Kristina Parkison. It's best for folks ages eight and older. Homemade dog snacks will be provided. Rain would cancel it.

The hike is free of charge. Sunol has a parking fee of $5 per vehicle. For information and registration, call 888-327-2757. Select option 2 and refer to program number 30734.

HIKE FOR WOMEN: "Women on Common Ground" is naturalist Katie Colbert's program for women who enjoy the outdoors but have concerns for personal safety. Katie will lead an easy four-mile hike through the oak savannas of Morgan Territory Regional Preserve east of Mt. Diablo from 10 a.m. to 2 p.m. Nov. 17.

The hike is free, but registration is required. Call 888-327-2757 and refer to program 30702. For hike information, call 510-544-3243.

walk the cemetery: There's a story, often tragic, behind every grave marker in Rose Hill Cemetery at Black Diamond Mines Regional Preserve in Antioch.

Naturalist Eddie Willis will lead a walk to the cemetery from 10 a.m. to noon Sunday, telling stories of the miners and their families who are buried there.

The hike is free. Meet Eddie at the parking lot at the end of Somersville Road, four miles south of Highway 4 in Antioch. Black Diamond Mines has a parking fee of $5 per vehicle when the kiosk is staffed. For information, call 888-327-2757, ext. 2750.

CHECK OUT THE CAVES: This is a good time of year to visit Vasco Caves Regional Preserve south of Brentwood, when the grass is starting to turn green and the vernal pools are beginning to fill with water. Besides the spectacular rock outcrops and Native American pictographs, there's a chance to see eagles and other raptors.

Vasco Caves is accessible only by guided tours, which are restricted to ages 10 and up, and cost $30 per person ($34 for nondistrict residents).

There may still be room on tours scheduled for 9 a.m. to 2 p.m. Dec. 2 and Dec. 15. For information and registration, call 888-327-2757. For Dec. 2 refer to program number 30708. For Dec. 15 it's 30710.

SUMMIT WILDCAT PEAK: For a climb to a great view, join naturalist Trent Pearce on a three-mile hike from 11 a.m. to 2 p.m. Sunday to the top of Wildcat Peak at the Tilden Nature Area in Berkeley.

There's a 360-degree panorama encompassing Mt. Diablo, Mt. Tamalpais, San Francisco Bay and the Golden Gate. Trent will talk about the area's natural and cultural history along the way. Bring lunch.

Meet at the Environmental Education Center at the north end of Tilden's Central Park Drive. Bring lunch. For information, call 510-544-2233.

big trees: Giant trees and rare plants are the themes of a couple of hikes scheduled in the Oakland hills this weekend.

On Saturday, naturalist Michael Charnofsky will lead a walk from 10 a.m. to noon at Roberts Regional Recreation Area and Joaquin Miller Park to find evidence of the huge redwood trees that grew there until the 1850s. The hike is for ages 10 and older. Meet at the main Roberts parking lot, which is off Skyline Boulevard about a mile up the hill from the intersection with Joaquin Miller Road.

Then from 10 a.m. to noon Sunday, naturalists will lead a moderate, 2.6-mile hike through Huckleberry Regional Botanic Preserve in search of the rare plants that grow there.

Meet at the preserve entrance on Skyline Boulevard about half a mile south of the intersection with Grizzly Peak Boulevard. Dogs are not allowed in the preserve. For more information, call 510-544-3187.

Ned MacKay writes a regular column about East Bay Regional Park District sites and activi- ties. Email him at nedma- ckay@comcast.net.