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Some Like It Hot: Wine Country Hot Springs
— Napa, Sonoma, & Marin


After a long day of travel, touring or wine tasting, there’s nothing quite like a soak in a natural hot spring to rejuvenate body, mind and spirit.

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  • Writer
    Russell Warner

After a long day of travel, touring or wine tasting, there’s nothing quite like a soak in a natural hot spring to rejuvenate body, mind and spirit. People have long gravitated to the curative bliss of hot mineral springs. Hot springs have been a solace to the soul for all of history, from ancient indigenous peoples, to early American settlers, to present-day populations. Thanks to its unique geology, northern California wine country is blessed with an abundance of these natural wonders. 

Wine Country Hot Springs

Within Napa, Sonoma and Lake Counties there are 44 named hot springs and two known geothermal resource areas (KGRA). The temperature of area springs ranges from a warmish 68 degrees Fahrenheit to a boiling 212 degrees Fahrenheit. Of special note to wine country trekkers is the Calistoga KGRA, the geothermal source feeding the many mineral springs and wellness spas in and around Calistoga. Sitting at the north end of the Napa valley wine trails, Calistoga hot spring spas offer the perfect beginning or end to a wine-country day. For more than a century, people have been coming here to enjoy the restorative powers of the waters in Calistoga, one of the nation’s most historic spa towns. And given the proximity of the Calistoga KGRA, it is hardly a surprise that there are numerous opportunities for a hot soak, a mud bath or a steam.

If you’re curious about why hot springs are hot, read on to the geology section at end of the article. But first things first, let’s fill you in on some of the area’s hot springs resorts and spas! With the range of special services offered by each, you are sure to find the perfect relaxation spot.

Napa County—Calistoga

For its 1950s-vintage-looking neon sign alone, Dr. Wilkinson’s Hot Springs Resort ranks as one of the prime destinations of choice. This Calistoga institution, situated in the heart of the historic district, has been providing visitors natural, simple relaxation for more than six decades. From a mud bath of pure volcanic ash (mixed with the “secret ingredient” of Canadian peat) to cleanse and smooth the skin, to a soak in a hot mineral-water whirlpool tub followed by a blanket wrap for a slow cooldown and a massage for ultimate relaxation, there might not be any more restorative ritual around. The facility also has two sparkling outdoor mineral pools for swimming and relaxation, and an indoor hot mineral pool.

As the oldest continuously operating pool and spa in the state of California, the 17-acre Indian Springs Resort and Spa offers a casual, low-key atmosphere that encourages relaxation and well-being. Four geothermal geysers produce mineral-rich waters that supply the mineral pools and steam rooms. Calistoga volcanic ash combined with mineral water creates the special mud for the purifying mud baths. The pools at Indian Springs are kept at 82 to 102 degrees Fahrenheit depending on the season and are kept open well into the night for a unique “under the stars” soaking experience. Around the corner is Sam’s Social Club, an on-site restaurant with a large, beautiful patio for alfresco dining. It offers artisan cocktails, local wine and craft beer, and a seasonal menu. Named for Samuel Brannan, the resort’s historic founder and early California entrepreneur, Sam’s has become a favorite of Calistoga locals.

Many other spas in the Calistoga area offer their version of mud baths, steams, whirlpools and massage. Among them is Calistoga Spa Hot Springs. It has four outdoor mineral-water pools ranging in temperature from 80 to 104 degrees Fahrenheit, and it offers mud baths and mineral whirlpools in its modern spa facilities. Roman Spa Hot Springs is an all season resort offering an outdoor natural hot-mineral-spring pool, mud baths, massage, facials and other spa services. And not to be forgotten is the Mount View Hotel and Spa, a 100-year mainstay of Calistoga hospitality. This historic Napa Valley hotel, a registered landmark on the National Registry of Historic Places, offers a variety of body wraps, scrubs, mineral baths and other spa treatments. For those who love a hot soak, there is something for everyone in Calistoga, from the casual, laid-back vibe to ultra-exclusive “million-dollar” experience, and everything in between: find your groove and take a soak.

Sonoma County

Those seeking the hot springs and spa experience in Sonoma County are also in luck. At the turn of the twentieth century, hot spring resorts of the county were popular vacation destinations for those seeking the curative effects of the waters. Though hot spring resorts and recreational facilities were more prolific in the past, travelers can still find them throughout Sonoma County. 

One of Sonoma County’s most legendary hot springs is Boyes Hot Springs, at the lush and elegant Fairmont Sonoma Mission Inn & Spa, just north of the city of Sonoma. Built in 1927 in a style intended to replicate a Spanish mission, the property was renovated in the 1990s and a new thermal mineral-water source was fortuitously discovered 1,100 feet below the hotel shortly thereafter. The resort offers six geothermal pools and a variety of spa treatments. A bit farther north, at the site of the historic Agua Caliente spring, is the Sonoma Aquatic Club. The facility offers three outdoor mineral pools, an indoor mineral pool and an outdoor Jacuzzi. While it is a membership-based club, it offers day rates for area visitors. And between Kenwood and Glen Ellen a refreshing soak can be found in the sparkling bathing pools of Morton’s Warm Springs Resort. Set on some 20 acres of forested hills, and bordering Sonoma Creek, Morton’s three mineral pools average temperatures between 82 to 84 degrees Fahrenheit. More fun day camp than spa, this seasonal family-friendly recreational facility features hiking and biking trails, sports courts, playgrounds, picnic sites and other amenities.

The one spa experience not to be missed in Sonoma County is the one-of-a-kind Japanese cedar enzyme bath at Osmosis Day Spa Sanctuary in Freestone. While similar to a mud bath in concept, the cedar bath therapy uses a dry fragrant mixture of ground cedar and rice bran as the therapeutic “soaking” medium. The body is entirely immersed in the cedar; the natural fermentation of the mixture warms the body internally, stimulating metabolic processes and circulation, and instilling a deep sense of relaxation. A bath attendant assists with cool cloths to the forehead and sips of water while you rest or gaze meditatively out into the tranquility of nature through the open-sided bath house. The cedar enzyme bath can generate a surprising amount of heat but does not feel suffocating or confining because the cedar is rather soft and fluffy. If you feel too warm at any time, you can easily move your arms or legs or adjust your position to unbury a bit. In addition to the internal cleansing benefits, the living enzymes in the cedar mixture do wonders for your outside by deeply and thoroughly cleaning the skin. Bathers attest that you will emerge from the treatment with your skin feeling soft, supple and nourished, and looking radiant. 

Osmosis also offers a variety of Eastern and Western massages and other spa services. For a special treat, pair the cedar tub with a massage in the outdoor pagoda, where you can enjoy ultimate relaxation, surrounded by the sounds and beauty of nature. The grounds at Osmosis contribute to the entire experience. The property is extensively landscaped and has walking paths, resting and relaxation areas, meditation spaces and five distinct types of Japanese gardens. Soaking, while enjoying the beauty of nature, is a perfect way to prolong the bliss of the day.

Ancient peoples to modern ones have regarded hot springs as sacred: special places to cleanse and purify body, mind and soul. The magical alchemy of a hot-spring experience induces a sense of peaceful well-being that’s difficult to adequately describe. The musings of Steven Spurrier, a character in the movie Bottle Shock, may express it best: “It awakens some ancestral . . . some primordial . . . anyway, some deeply imprinted and probably subconscious place in my soul.” Although he was waxing poetic about wine, the words apply equally well to the universal attraction to hot springs.

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Why Hot Springs Are Hot

Although the sun heats the atmosphere, the sun -- contrary to popular belief -- does not significantly heat the earth. The sun’s heat penetrates only a few feet into the earth’s surface. Instead, the earth is heated from its own internal heat sources, which create what is known as the geothermal gradient: increasing temperature with increasing depth from the surface into the interior. The geothermal gradient reflects heat flowing from the extremely hot interior and cooling off as it moves to the surface. Near the surface of the continents, the geothermal gradient is about 1.5 degrees Fahrenheit for every hundred feet of depth into the earth. The shallow ground, essentially the upper ten feet of the earth’s surface, maintains a near-constant temperature of between 50 and 60 degrees Fahrenheit. The ground surface is part of the earth’s outermost layer, called the crust. Earth’s crust varies in thickness, from as little as three-miles thick on ocean floors up to about 40-miles thick in mountainous regions. 

Below the crust lies the mantle, a massive 1,800-mile-thick layer of hot rock. The mantle continuously produces heat due to the decay of naturally occurring radioactive elements in mantle minerals, principally thorium, uranium and potassium. Radioactive decay from these unstable isotopes releases heat, and that heat (in addition to contributing to the geothermal gradient) fuels movement of the plastic mantle, which is what drives movement of the world’s crustal plates. Some of the hottest underground temperatures are associated with “hot spots,” areas of volcanic activity that occur at tectonic plate boundaries and at places where the crust is thin enough to let heat through. Earthquakes occur at and near plate boundaries where movement causes breaks (e.g., cracks, fissures, fractures and faults) in the earth’s crust which act as avenues for geothermal underground waters to circulate toward the surface. The result is hot springs, geysers, fumaroles and other geothermal surface features.

A hot spring by definition is a spring with water at temperatures noticeably higher than ambient air temperature. Hot springs are common in areas where geologically recent volcanic activity has brought magma (molten material beneath or within the earth’s crust) close to the surface of the earth. One example is the Mammoth Lakes area of Mono County, in the eastern Sierra Nevada region of California, where a chamber of magma lies about three miles below the earth’s surface. The magma heats underground aquifers, and faults and fissures in this volcanically active area provide numerous pathways for the geothermal waters to circulate to the surface. This creates many warm and hot springs, such as those in Hot Creek in the Inyo National Forest, where pools of water literally boil. In years past, one could soak in hot spring pools on the banks of Hot Creek, while a few feet away, the cool waters of the creek supported a trout population. But the springs and geysers in the streambed and along its banks now change location, temperature and flow rates so frequently, quickly and unpredictably that the Forest Service determined it was no longer a safe place for bathing. The Hot Creek Geologic Site maintained by the Forest Service is still an interesting and beautiful place to visit, but soaking in the hot springs is no longer allowed. The boiling hot springs and violent geysers of Hot Creek are visible signs of the volcanic processes that are at work.

The other way geothermal water is generated for hot springs is through convective circulation, generally in non-volcanically active areas. In the convective cycle, gravity combined with recharge (the absorption of ground water) from snowmelt and rain at high elevations causes water to migrate from the surface of the earth deep into the crust, where the temperature of the rocks is high due to the geothermal gradient of the crust. Water coming in contact with the heated rock formations expands and becomes saturated with minerals from the rocks. This superheated water is less dense than cooler, heavier water percolating down around it. As the cooler water sinks, the hot buoyant water rises creating a convection cycle that drives the superheated water to the surface moving through faults, fractures and other vertical pathways through the crustal formations. The convective process takes thousands of years.

Hot springs are the magic that results when all of the components align: heat and water and the earth’s natural plumbing. And at the end of an active day, there may be no better way to rejuvenate and recharge than with a long soak in hot mineral-rich water, compliments of Mother Earth.

Russell Warner, a geologist and geochemist for 35 years, has a lifelong interest in science and nature. He has visited natural hot springs in Alaska, Arkansas, California, Colorado and New Mexico.

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