There are two species of redwoods in the US — giant sequoias (Sequoiadendron giganteum) and coastal redwoods (Sequoia sempervirens). They are in the same family, but different genera. (The used to be considered part of the same genus long ago, but not now.) Sometimes you hear the names sequoia and redwood applied interchangeably, but I’ll use these words here as shortcuts for the longer names above. (That is, "sequoia" = giant sequoia, "redwood" = coastal redwood.)

size:
sequoia: considered the most massive species on earth, with the biggest diameter trunks
redwood: considered the tallest trees on earth

(Sometimes people propose that other species are the champions, but I’ll ignore that here. Even though the tallest redwoods are taller than the tallest sequoias, sequoias are also very impressively tall. And even though the biggest-diameter trees are sequoias, some redwoods have very impressive diameters. In short, both trees are massive in all respects.)

locations and growth pattern:

Redwoods grow in dense groves in which they are the dominant trees. These groves are usually located at lower elevations in the coastal range of California, from the Big Sur region to the Oregon border. The trees grow naturally only in the fog belt region near the coast, where their huge height helps them absorb water from fog during the dry summer months.

Sequoias grow in isolated groves in the middle altitudes of the western slope of the Sierra Nevada (the highest and most impressive mountain range in California). Within these groves, they are intermixed with other species of trees. These other species are sizable, but they tend to look like toothpicks when you see them alongside the giant sequoias.

leaves:
Redwood leaves are arranged in flat sprays of linear leaves near the bottom, but in awl-shaped leaves that cling closely to the branch near the top. Interestingly, the leaves of giant sequoias closely resemble the leaves on the upper branches of redwoods. Both trees are evergreen.

logging:
Redwoods are known for producing high-quality wood, and that’s why most of California’s old-growth redwoods have been chopped down (but what’s left is preserved in many beautiful parks). When San Francisco was rebuilt after the 1906 earthquake and fire, the rebuilding was done largely with redwoods. Sequoias have been logged in the past, but I don’t think its lumber is very useful.

age:
Both trees live tremendously long. The oldest redwoods are about 2000 years old, and the oldest giant sequoias over 3000 years. Surprising, they’re not the oldest trees in California. The bristlecone pine — a far less imposing tree in the mountains of eastern California — can live over 4000 years.

As for where to see them, you have lots of options. For redwoods, the simplest one is to visit Muir Woods, which is a short but twisty drive north of San Francisco, and which is a major tourist attraction. The main trail is paved and handicap-accessible. If you have your own wheelchair, you can use that. Otherwise, I think that the park staff probably has wheelchairs to lend to visitors (but you should call them to ask).

You have several transportation options for Muir Woods:
1) Drive. The problem is that the parking lot gets very crowded, and many people park far away and walk in. I recommend that you call them and ask about the availability of handicapped parking (and how difficult it is to get one of those spots). The best bet for parking is if you arrive early or late in the day.
2) Tour bus. Many tour bus companies take people to Muir Woods (sometimes combined with other destinations, such as the wine country or Sausalito).
3) During summer months, a third option is to park a few miles away and transfer to a shuttlebus.

There are lots of other beautiful redwood parks, although some may not be wheelchair-friendly. Two outstanding ones are Big Basin Redwoods State Park in the Santa Cruz Mountains (south of San Francisco) and Humboldt Redwoods State Park (a long drive north of San Francisco). Even farther north is Redwood National Park along with three very large state parks.

(Warning: Governor Schwarzenegger is threatening to close nearly all state parks, and it is not yet certain how this will play out. The national park system, however, will not be affected, so Muir Woods will remain open.)

For giant sequoias, there are quite a few groves in the Sierra Nevada, roughly five to seven hours’ drive from San Francisco. Three excellent ones are the following:
– Calaveras Big Trees State Park
– Mariposa Grove of Giant Sequoias in Yosemite National Park
– Giant Forest in Sequoia National Park

Because giant sequoias grow several thousand feet above sea level, snow makes them largely inaccessible much of the year. A good time to visit is from around May to early- or mid-October.

The Mariposa Grove in Yosemite has a shuttle bus; so even if a visitor can’t walk, he can ride the bus and get good views of the trees.

The closest places to stay to visit the Mariposa Grove are the following:
– Wawona Hotel (in the park)
– the towns of Fish Camp and Oakhurst, south of Yosemite National Park
– lodgings in Yosemite Valley (spectacular views, but overpriced and difficult to get reservations)

There’s a third species of redwood which is native to China — the dawn redwood (Metasequoia glyptostroboides). Unlike California’s two species, this one is deciduous. There’s a very interesting story behind the discovery of this tree, but that’s a major digression.

Your question mentions "misty forests." In that case, you’re talking about the coastal redwoods, since they grow in the fog belt near the California coast. (It’s possible to have fog in giant sequoia groves, but it’s not common.) Of course, the redwoods are not always in fog, and most often the fog is more like a low cloud that hovers near the tops of the trees, with good visibility at ground level. Still, they are very beautiful when shrouded in fog, as is a redwood forest when shafts of sunlight beam through the dark trees.

Coastal redwoods are accessible year-round, but the persistent coastal fog is a summer phenomenon. Summers are dry and foggy (with the fog often burning off mid-day); winters are rainy, with really nice days between the rainstorms.

If you need any other information, feel free to add more to your question or drop me an email.

They are very similar, but the Sequoias are the biggest trees. I have seen them in Yosemite, and Sequoia and Kings Canyon National Park. You can see them in either place if you have limited mobility. To see some of the best redwood forests, go to Muir woods in Marin county, California. They are not the biggest, but the most beautiful. For the biggest redwoods you would have to go way up in Northern California to the Avenue of the Giants in Humboldt county.

There are two types of Redwoods in California (of the three in the world). The Giant Sequoias are found on the western side of the Sierra Nevada mountain range. The Coastal Redwoods are found in the Coast Range. The trees are a bit different, but the environment you find them is very different. The Coast Redwoods are found in cool wet forrests with ferns and banana slugs. The Giant Sequoias are higher and in wamer, dryer forrests with pine trees.