I will echo a bit what Al has said: Yosemite in one day will be no fun. Leaving from SF and driving by car or bus is a 6 hour round trip. June is a summer vacation month so the park will be a lot more crowded as will the roads going to the park. And you mention that you will have children with you also, it will be a long and tiring day for them and having raised 4 children they probably will not be pleasant at the end of the day.
Saying all that you will probably still go to see the sights and say you have been there. It is a magnificent park. My wife and I stayed outside the park for 3 nights back in October, 2010 and enjoyed it very much. To leave the hassle of driving that far just for one day I would do the tour bus for your family. I don't know anything about private tours.
UPDATE: August 25, 2006, Hwy 140 is now partially open in daylight hours, but CLOSED at night.
This is a temporary warning, mainly aimed at any traveler entering Yosemite National Park in 2006 (and possibly 2007): HWY 140 BETWEEN MARIPOSA AND EL PORTAL (meaning the Arch Rock Entrance) IS CLOSED. There has been a major rock slide that, as of late June 2006, is still active. This closure will probably last the rest of 2006 and may continue into 2007, since a large part of the road will have to be completely rebuilt. El Portal, however, is still open, as is Mariposa. If you are entering the park, use either Hwy 120 (Big Oak Flat Road) or Hwy 41 (Wawona Road).
We did not know about the tire chain requirement when we were here in December 2003. There was a big snowstorm a day before and we were trying to enter the park via California Highway 41 from Oakhurst. As we drove the mountainous, winding roads, the elevation increased and heavy, deep snow started to appear on the side of the roads. Near Fish Camp, the traffic had stopped and apparently there was a ranger who was checking each vehicle for tire chains and each vehicle was required to put them on. We did not even have tire chains so we had to turn back and since we are from the Midwest and hate driving in snow, we decided not to visit the park. I'm not saying that you shouldn't visit Yosemite during the winter; it's probably very beautiful. Just be prepared to encounter winter weather and do have tire chains in your vehicle!
such a madness!!!! this is a proper word to identify how so many people drive their cars, vans o RV. I guess that max speed is 40 or 45 miles per hour because there are some risk of bear crossing...actually main cause of bears death is for drivers who run over them. So almost nobody respect that speed .. no paying attention laws and wildlife.. its a pitty and I shame on them
Be careful when you drive to Yosemite. It is curve after curve for miles. Especially going South from Yosemite Valley.
A lot of drivers become impatient so you can use the pull outs. Reduce you speed when pulling over so you don't go over the edge of a cliff.
Each winter, the Sierra Nevada recieves a large amount of snowfall (150+ inches), which will usually shut down many roads and trails in Yosemite National Park. This means that visitors in winter will not be able to reach places like Glacier Point, Mariposa Grove, and Tuolumne Meadows. Here is a bit of information about what's closed and what's not in winter:
Yosemite Valley: Open year round, roads are plowed in winter though chains may become necessary. The Mist Trail from it's first junction with the John Muir Trail to the top of Vernal Fall and the John Muir Trail from Clark Point to the top of Nevada Fall are closed in winter, and the cables ascending Half Dome are down.
Hetch Hetchy: Open year round, though a major snowstorm may cause the road to close temporarily; reduced hours in winter.
Glacier Point: The Glacier Point Road is usually closed from late October-early November to May. In 2006, the Glacier Point Road was opened on May 24. The Glacier Point Road is kept open to Badger Pass during winter.
Mariposa Grove: The Mariposa Grove Road is closed November to April. Plowing starts after snow stops.
Tuolumne Meadows: Tioga Rd is closed from Crane Flat to Lee Vining from late October to May. This is not definite; sometimes snow doesn't come until late in the season (one year, the road wasn't closed until January 1st the next year), and sometimes it snows alot (another year Tioga Rd wasn't open until July 1). In 2005, Tioga Rd was open on June 23, in 2006, on June 17; plowing usually begins on April 15, but on years of heavy snowfall this will be delayed to May 1. Plowing the road takes about 45 days, if there are no major avalanches.
Note that Yosemite's High Sierra Camps usually won't be open before July 1, and that on years of particularly heavy snowfall (like 2005), they were closed for the season.
If you're frustrated by the 35 mph signs on roads in the park and would like to go faster, remember that the speed limit is to protect wildlife, not you; national parks don't just preserve scenery, but the everything natural within its borders. Deer and other animals react with bad judgement when they see cars coming, and speeding will not give them enough time to escape. If you hit a deer, not only will the animal die, your car will be heavily damaged. Also, on Tioga Road, slow down for bears! Every red bear sign you see on the roadside signifies that a bear was hit and killed by a car there. Remember that this is their home and not yours.
Tioga Pass, the main entrance into Yosemite National Park from the east, is at a high altitude (over 9000 feet). As a result, it is often closed until late May or even June due to heavy snows that take a while to melt or get cleared.
You may want to check the National Park Service website for road construction and/or closures. When visiting in late May, early June the asphalt roads in Yosemite Valley were being slurry sealed and it was common for one lane to be closed off. Delays were from 5 to 30 minutes and a few times I turned off my engine if it appeared to be a long wait. Not sure if they were trying to complete the roads before the height of the summer season or if construction is on-going.
You can't help but feel tiny when visiting Yosemite. The surrounding rock faces and sheer size of the park account for that meager feeling. The vastness will certainly be an amazing feeling but a few problems arise from it.
1. With everything so far away (30-40 miles from park entrance) it will take you a long time to travel from place to place. The trip to Glacier Point from the valley floor for an example is an hour each way. The idea here is to give yourself a lot of time.
2. Unless you have a very fuel efficient car you will use more than half a tank of gas in the park. The main problem here is that their were only two gas stations in the park. Both near entrances and the gas at them was priced about a dollar higher than the current gas prices elsewhere, so try to fill up before you enter.
Their are a lot of very long stretches of downgrades In Yosemite. The worst of which would have to be the road down from Glacier Point. When you are traveling down that and other long hills you may want to downshift. The continual use of your brakes could very easily render them useless.
Yosemite's roads are filled with debris such as tree limbs and the occasional falling rock. I'm not exactly sure what ripped a hole in this tire, but it surely put and end to sightseeing that day.
If you find yourself in a similar situation, please note that there are no full service gas stations or other facilities within 30 miles of Yosemite. The closest place to get a new tire is Oakhurst, south of Yosemite, no matter what the rangers may tell you. Yosemite Village has a gas station and can change a tire, but if its a serious repair, you're out of luck.
Plan your driving time well. There are no lights on the road at night and the roads get confusing. Get up there before it gets dark, or else you are driving in absolute pitch black... can't see 5 feet in front of you.. also this makes it hard to set up a tent/fire with only a flashlight.
Getting to and from Yosemite is a long drive from most places, and drivers tend to get ansty and want to drive fast by the time they're at the park (or readying to leave). Most of the time, in the valley, there are only two lanes, and lots of people and ANIMALS walking near or on the road.
Please try to be patient, not speed and keep an eye out for "scamperoffs" (the creatures that jump on the road and dash off quickly).
Once you get into Yosemite National park, you will be treated to long, and winding roads, frequently with blind corners. Be very careful especially at night and when it rains. The roads can sometimes be quite narrow. I remember one nasty turn when we were driving up to Glacier Point, where the road curved sharply and if you were driving any faster than 20mph... well lets just say that there's no guard rail and its a long, long, long way down. So drive slow and carefully... there's no need to rush, Yosemite ain't going anywhere.