Safety
The regions North of the Yukon River, all the way to the Arctic, are the worst for mosquitos in general. The worst time of year to go is in July, however you are likely to encounter them as soon temperatures remain above freezing for a couple of weeks.
You can bring repellant, but the stuff that repels the best is bad for your skin and clothes, and will contain a measured amount of deet. Since I personally prefer to not to crop dust myself, you can purchase netting to go around your hat or head, and maintain long sleeves and pants throughout the day.
If you still get bit, don't scratch!
Hi Grace,
You're in for a treat. Yosemite is in full swing (including Mariposa Grove) during Thanksgiving week. In fact, it's a beautiful time to be there. If you're in need of a place to stay, consider the Evergreen Lodge and see this link for their Thanksgiving activities.
Have fun!
Yes, however the last mile of road is very narrow, and has two hairpin turns. We drove a truck and 12ft trailer (24ft total length) and have to slow down to less than 5mph to make the turn. Buses go up there all day long, but be patient with other vehicles who do not realize that they have to stop and wait for you to pass before they can use some of the turns. If you are towing a smaller vehicle, I would advise you to use this when going on any excursions in the park.
Also, do not enter/exit the park via 140!!! There are vehicle restrictions for personal vehicles over 40ft. On that side of the park there was a rock slide several years ago, and a temporary bridge is in place. Consider alternate routes into/out of the park.
You may bring your dog to Yellowstone as long as you follow park regulations and take safety issues into consideration. Pets must be on a leash at all times and may never be left unattended.
Make sure you read ALL of Yellowstone's rules about pets before deciding to bring your dog to the park.
You've got a popular question! Check out the answers to this similar question for tips.
Pets are allowed in Yosemite only on fully paved trails and roads except trails signed as not allowing pets (pets are not allowed off the floor of Yosemite Valley, including the trail to Vernal Fall).
Pets are not allowed on unpaved or poorly paved trails, or trails signed as not allowing pets. For an entire list of pet-related regulations at Yosemite, visit nps.gov.