The high country is amazing, but it is heading towards winter, and snow is possible. Yosemite Valley is great any time of the year. I'd plan on a day in the valley and camp there at night. The Mariposa grove of Giant Sequoias is great to visit. A drive on the Tioga Road (Route 120) to Tuolumne Meadows has amazing scenery. Day hikes, or overnight hikes, from here bring you to the high backcountry, but you need to be prepared for bad weather and should be experienced.
The National Park Service website has a lot of information for first time visitors.http://www.nps.gov/yose/planyourvisit/things2do.htm
October 2009 - N.P.S.
Half Dome Cables
The Half Come Cables will be taken down on October 13. When the cables are being taken down, all access along the route will be closed.
Tioga and Glacier Point Roads
From October 15 until the roads open in the spring, it is illegal to leave vehicles parked overnight along the Tioga Road between Crane Flat and Tioga Pass, or along the Glacier Point road east of Badger Pass, or at trail heads or any other area accessible from these roads.
If you are planning a hike from these roads after October 15, please arrange for drop-off or pick-up transportation. In addition be prepared for the possibility that the Tioga or Glacier Point Roads may be closed due to snow and that you will have to hike to another road or developed area that is open.
All bus services to Tuolumne Meadows and in the Tuolumne Meadows area are closed for the season. Furthermore, all facilities except the gas station and wilderness center are closed in Tuolumne Meadows. The Glacier Point Tour Bus will remain operating until the Glacier Point Road closes.
Bears are active in Yosemite’s wilderness. There is high bear activity in the Glen Aulin and the Little Yosemite Valley/Sunrise Creek area. Please remember to store all your food and scented items in bear canisters or food storage lockers to protect the wildlife. Whenever food or scented items are out, please keep them within arms reach, even while day hiking.