Novato & Fairfax have dozens of great hiking trails that are dog friendly.  A great guide to the many dog friendly beaches and trails is found on the Marin Visitors Bureau website. Below are a few highlights.

The Cataract Falls Trail is a good one for January-February because the water will be really flowing. Of course wear good hiking shoes since the trail is bound to be slippery in spots. Parking is limited, but this out-and-back 2.6 mile hike is worth the effort. Dogs are allowed on leash, but they should not go into the water since the creek feeds into a water supply.

Hiking in the Indian Valley Open Space in Novato is a fun one for dogs. They can be off-leash on the wide, flat fire roads, and in the winter you can see the waterfall. You can see horses and bicyclists here as well so if you go on a busy weekend you may need to leash up any herding dogs.

Two Lakes Trail isn't the name of a trail, but it refers to a popular and dog friendly hike around and between Bon Tempe and Lagunitas lakes in the Mount Tamalpais Watershed. This one is a moderate hike of about 2.5 miles with only a 200ft elevation gain. Dogs should be kept on leash and out of the water.

A great stop for dog friendly shopping and dining is the Marin Country Mart in Larkspur. You must stop in at the George pet shop to get some amazing toys & treats for your pup. Beach BBQ Bits jerky treats are sold here!

The Mart also hosts a Farmer's Market Saturdays 9a-2p, Jazz Concerts on Friday nights and the Folkish Festival on Sundays. This is also a great ferry stop for San Francisco, but dogs are not allowed on the ferry so arrange for doggie day care if you can.
Hiking in Marin County
Point Reyes National Seashore in Inverness allows dogs on leash on three beaches: Kehoe, Limantour and Great Beach. There is a great deal of wildlife and marine life in the preserve so dogs are restricted for that reason. However, it is a unique and beautiful coastal area not to be missed.
December-March you can view the Elephant Seals at Chimney Rock, and starting in mid-January you can watch the Gray Whales migrate along the coast.  

Three nearby beaches are off-leash for dogs: Bolinas beachDillon Beach and  Muir Beach in Sausalito.

The Cottages at Point Reyes Seashore offer a great dog-friendly lodging after a long day of exploring.  Besides having a spacious green area to walk your dog, they also have a dog run.  Dogs must be well-behaved. The Tomales Bay Oyster Company is a truly unique and dog friendly picnic spot  where you can shuck your own oysters. Grills and shucking knives are provided, but you should bring your own drinks, sides, plates & utensils. Limited parking. The historic Farm House restaurant in Olema is another great place for breakfast, lunch or dinner. Dogs are not allowed in the restaurant so it's a good stop after a day of hiking. Find time to stop and shop at Toby’s Feed Barn at Point Reyes Station. One of a kind gifts, pet food and organic produce make for great souvenirs. 

Top Dog Friendly Restaurants: Tomales Bay Oyster Company, Nicke's Cove, Left Bank Brasserie, Marin Brewing Company, Toast

Top Dog Friendly Hotels: Cavallo Point, Nick's Cove, The Cottages at Point Reyes, Rosemary Cottages, Tomales Bay Resort, Dillon Beach Resort

Doggie Daycare:Canine Cove, Camp K-9 of Marin, 
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