1

The northern California coastline would be a better choice.

2

Climb Mt. Shasta? Backpack on the Pacific Crest trail?

Redwood State & National Parks. the average high temperature i Eureka in August is 64. Expect fog. Might even rain.

Mark Twain never said "the coldest winter I ever spent was a summer in San Francisco," but that's another possibility.

3

Lassen?

4

You dont say where you are coming from, so dont know what is convenient to you, also what you want to do when you get there (camping or 5 star hotel,- Hiking, museums or strip clubs). Sticking with California options,Tahoe is another nice higher elevation destination that has it all. I like the north coast Arcata/Erueka area. Avg temps in the 60's in July, with cool ocean breezes with plenty of accomodation options and visiting the beaches and redwoods to pass the days.
Something closer to S.Cal is San Jacinto State Park, on the mtn outside Palm Springs, its at 10,000 feet in elevation. You can drive up or take the tram, and camp, get a cabin, or get a room at nearby towns like idyllwild

5

I thought of Lassen, but the forecast temperatures for the next few days are in the high 70s at 6500 ft, and high 60s/low 70s at the peak, so I figured it doesn't qualify as "cold." Same with South Lake Tahoe.

The summit of Mt. Shasta will have a high of 39 on Tuesday, with wind.

6

The weather right now at Lassen is 10-15 degrees warmer than normal for this time of year, It is usually cooler. However there is no real accomodation except Drakesbad and camping in the park, and even then the camping sites are not up at 10,000 feet, but rather at the lower elevation/warmer parts. Tahoe is lower than Mammoth Lakes, however there are several destination in the basin, such as Squaw Valley, which are much higher in elevation. We still dont know if the OP wants to camp, or stay in a hotel.

7

Crescent City, CA

For the next 10 days, the highest temperature forecast is 63 and the lowest is 48. Nice and cool, I think.

8

I agree, redwood country is where it's at for summer coolness.

9

Weather.com calls for highs ranging from 73 to 81F over the next 10 days. In Arcata, highs ranging from 56 to 63.

You want to travel sometime in July or August or stay someplace for both months? Big difference. What's your budget? What do you want to do? I think we're guessing you're in Southern California, due to mention of Mammoth Lakes. Not exactly cool there (San Diego and Santa Monica would be cooler, unless, of course, you backpack into the High Sierra), and pretty hot on the way. Northern coast would be a long drive, but obviously cooler. Need more info from you.

10

Fair warning: Mammoth Lakes could be wicked hot in July/August compared to so many other California locations. To generalize: for cooler summer destinations, stick to the coast, and the further north you go, the more cool weather/fog you'll encounter. Fog early in the day burns off for glorious yet not-hot afternoons and cool evenings. Even if there are consecutive sunny days that don't start off foggy to keep the days cool, those don't last for long. And those sunny days will still be way cooler than anywhere you'd be further inland where it will be hotter still!

Now, it depends upon what you want to do in California. If you want movie/TV/music industry, Disneyland and those kinds of attractions, you're sunk; July/August will be hot--no way around it. The nice thing is the water's warm enough for swimming in Southern California beaches. If you want spectacular nature and aren't looking for loads of cultural stimulation, then redwood country would work--but can get hot, too, so, again, stick to the coast--and Mendocino and Arcata are great for both people and to get your more civilized interests covered. San Francisco's cool summers would give you city-oriented attractions in a very scenic locale and near spectacular redwoods like at Muir Woods (for a mini redwood fix).

The trick will be finding someplace in California that isn't super crowded, especially cool locations, since, quite naturally, that's what we all seek. :) So, that being said--

I don't know where you're driving from, and to be honest if someone wants to get away from the heat in California in summer, I suggest considering Santa Cruz. A tourist destination since the 1800s for folks wanting to get away from the heat, I consider Santa Cruz to be an "Alice's Restaurant" kind of town ("You can get anything you want at Alice's Restaurant..."). Ocean, redwoods (actually, all kinds of outdoor interests--river, slough, lagoons, but the ocean and redwoods tend to take the cake), more than its share of culture and tech for the size of the town (thriving arts scene, good restaurants/bars/breweries, renowned wine area, requisite glut of coffee houses :) )...lots of other stuff, too--surfing, boating, and other sports; politics; technology and science--all kinds of stuff, and San Francisco is only about 70 miles away if you need a bigger-city fix. A university town, it's fairly laid back and mellow. Although it's changed markedly since its downtown had to reinvent itself after being destroyed in an earthquake 20+ years ago, it still retains some of the quirky elements with street performers and quasi-legal vendors amid the web entrepreneurs and ever-more affluent students. The temperate climate, both weather and socio-politically, also attracts a street element, which depending upon one's point of view adds to the color or the annoyance of the downtown area, but rarely any kind of threat. So, if ya want a one-stop destination for chill fun, I'd say grab a spot in the Santa Cruz area and once you're there ditch your car and grab a bike--as with anywhere in California these days, traffic's sucky...but a bike will do ya well. OK, so lotsa folks bike up to the redwoods, but unless you're in pretty dang good shape, ya might wanna take the car there...but for a lot of local tooling around, you'd be fine on a bike--it's a pretty compact area--and having traffic-free vacation time! Oh, and, no, I don't work for the local tourist industry...just MHO... :)

Wherever you go, hope you have a great time!

11

http://exploredelnorte.com/itineraries/High-Adventure-Majestic-Redwood-Forests-of-Del-Norte-County-Itinerary.html

http://www.allegiantair.com/

http://www.southwest-point.com/

http://www.transitunlimited.org/Redwood_Coast_Transit_20

12

Anywhere within 1/4 mile of the coast.