I'll add this in regards to California: some events (pro or sportive) don't even cover 1/5th of the great climbs available here. Similar to the ASO/TdF in that they can still pull out roads that have never seen the Tour yet and become legendary once they're televised, there are a lot of great places to go. The limitations are often weather/time of year and how much time you have.
For example, this route was done by a small group of us to test out an idea (5 total) last Fall: http://ridewithgps.com/routes/726236
It starts off on the Eastern side of the Sierra Nevada mountain range (most of which is taller than the Alps), crosses over to the Western side through a National Park - and then back. If you can arrange to have your things waiting for you in Yosemite National Park (at a campsite or the Wawona Hotel), it won't be nearly as difficult. But the climb from Hwy395 just to the gate of Yosemite is called Tioga Pass. The road through Yosemite will take you just short of 10,000ft
Sherman Pass is a little bit further South of that.
California as a whole:North
Countless roads with "major rolling climbs" and heavily shaded, deep forest, you're-the-only-ones-around"
Mt. Shasta area and anything west to the Coast.
Sierras North of Lake Tahoe are great
Tahoe Lake & vicinity is great for both road and mountain.
The area just south of Tahoe, around Markleeville, is home to many of the mountain passes used for Death Ride (difficult) and the Alta Alpina Challenge (very difficult)Mid-North/Bay AreaTerrible Two
is an event which covers an area just north of the Bay Area (San Francisco) - look up their route as they cover a number of great climbs on very single-lane-European style roads
Riding in Marin County is just plain amazing and gorgeous. There's a reason so many of famous frame designers and founders of the sport come from there.
Mt. Diablo is just a skip from Oakland, magnificent climb. Santa Cruz Mountain
range is to the South, a veritable playground (and testing ground for Specialized, Bell, Giro and Easton)
Hwy 1 (Pacific Coast Highway) mostly follows the coast and features steep rollers and dramatic changes in flora.South
Santa Ynez Valley is most often the place where both pro and amateur teams hold training camps. Plenty of roads & climbing, sometimes no traffic, and lots of wine.
Santa Barbara is a great little town featuring the famous Gibraltar Climb, called the "Alp d'Huez of North America" by some. US Postal used to do training loops of Gibraltar
/Painted Cave/San Marcos Rd twice, which comes out to ~7,000ft in 100mi, most of which is steep.
Hwy 33 out of Ojai. Go mid-week (Tuesday is best) and you won't see a vehicle for hours - and it's all uphill. It won't ever be ToC featured because it has to be done as a loop in order to get back to civilization, which won't make for a dramatic finish on television.
Santa Monica Mountains have too many climbs to count, most of which are Cat 2.
Angeles National Forest features many Cat 1 climbs, a few HC. Some have been in the Tour of California
San Bernandino Mountains have great climbs - Mt. Baldy for examplePalomar Mountain
- HC with Chris Horner as your current leader.
a little east of San Diego, the Cleveland National Forest has plenty of climbs to challenge you, most Cat 2 and of course gorgeous. Go in the early Spring.East
Riding Death Valley (it's a National Park) is simply monumental and deceptively difficult. Outstanding landscape. Most climbs are Cat 1 and HC. They would most likely never feature in the Tour of California though because it is a National Park, very remote for the general public, and weather-timing is difficult. Go in the Winter or very early Spring. Cross your fingers because some days may find 25mph+ headwinds no matter which direction you go.
...basically any road heading into the Sierras west of Hwy 395 will be Cat 1 or HC. There are too many to count. Late Spring or late Fall is your best bet to avoid heat, but you may find the top cut short with snow. If you climb in the Summer, your starting temp at Hwy 395 may be 90F with snow or hail at the top of the climb.
Mammoth Lakes, CA is a great resort town. During the Summer it is a cycling haven - open roads, plenty of climbing with a base
elevation of 6,500ft, and the entire mountain ski area is open for mountain riding. It is possible to do 100mi, 9,000ft of climbing and only encounter 3 stop signs for the entire ride. Loop over to June Lake for views so scenic you may consider just stopping for a few hours by a lake.Middle-ish
Sequoia National Park
King's Canyon National Park
Yosemite National Park
... and more in the area.
Use Strava's Segment explorer to see various climbs (it will only show the more popular ones however, there are more out there). For example start off with "Mammoth Lakes, CA" and then just move the map around.