When driving on Hwy-101 in northern California you MUST take the time to see the Redwoods. These giant trees can grow to heights of over 300′. Standing in a grove of these giants feels like standing in a sacred cathedral of nature. The road offers many sightseeing places and I only got to see a few so my list is far from complete.
Hwy-101 turns inland just north of Humboldt Lagoon. Look for the Newton B. Drury Scenic Parkway. From Hwy-101 take exit 753 if traveling north and exit 765 if traveling south. The scenic parkway takes you through an absolutely spectacular forest filled with groves of giant redwoods.
Take your time and stop at some of the parking areas and stroll on the trails and admire these wonders of nature. Be sure to see Big Tree which is close to 300′ tall, about 28′ in diameter, and roughly 1500 years old. Take care to treat these areas with extra measure of care and respect. Take only photos and leave only footprints.
Farther north on Hwy-101 (near Crescent City) lies the Jedediah Smith Redwoods State Park. The park contains many parking areas and trails that allow you walk amongst the trees. The Stout Grove is one of the particularly impressive groves. When observing the trees take a little extra time and look at the different styles of bark and how they vary from tree to tree. The bark on the same type of tree can vary significantly between individual trees. Some bark is smoother, some rougher, some in linear patterns, and others in more wavy patterns.
Be sure to enjoy and respect these areas. Remember that these trees are living and breathing organisms. Be sure to have a very wide-angle lens when taking photos (you will need it). If you have a macro lens be sure to look down for interesting photo opportunities including mushrooms, toad stools, leaves, leave skeletons, bugs, etc.