We did a similar trip at this time last year. We had our hearts set on a few places along the way (Big Sur, Santa Barbara) so prebooked those. And if you want to stay in or near national parks, reservations seem to be necessary almost any time of year. Otherwise, we booked a day or two ahead of time as we went. Internet booking often gets a better rate, and then you have the GPS locators to guide you into unknown towns and cities. We never had a problem. You can see our trip report under my screen name...

On our road trips, we book about 2 hours ahead . . execptions are in Nat'l Parks and cities where something big is going on ( which we generally avoid )

If a National Park is full, we check in along the way for cancellations . . has worked every time so far! We had to stay one nite outsice the Grand Canyon but finally got our two nites at ElTovar.

Sometimes we have to stop earlier than we would like, but have never not been able to find a decent hotel

Good advice so far. We often go without reservations so we can stay longer or not as the mood strikes us. You usually can find lodging near interstates at the intersections with numbered routes. I pick up the magazines like RoomSaver at welcome centers that give discount coupons for hotels/motels. They have maps that show the locations of places to stay. You can go on line and find them too. Even if we don't/can't use the coupon, the phone numbers for the places and what they offer for extras are usually printed, so you could call ahead for availability along the way.

You will probably need reservations to stay in Yosemite or Yellowstone. I've been lucky at Grand Canyon and walked in and scored a room several times in April.

Yellowstone will probably have very limited access as there will most likely be snow on many roads in April. Yosemite will probably only have the valley open, but the waterfalls should be great.

Thank you all for your very helpfull information. Looks like we will either book the night before or take the risk of finding something on the day. We don't need to stay in National Parks and will be lucky to already have free accommodation near Yosemite and Yellowstone which will be later on in the trip, being June.

Friendship_Bay
I have just finished reading about your trip. It sounds very much the way we want to go. Thank you for that.

You should consider adding Death Valley National Park to your list. It's only about a 2 hour drive from Las Vegas, and could be covered on your drive to or from LA.

Yes, we do plan on that as a day trip from Oakhurst where we have a weeks accommodation. Being from Australia we are used to big drives, but I hope not biting off more than we can chew.