National Forrest, Parks and State Parks

Much also depends on what you consider good enough. If you need a pad length that will accommodate the full length of your trailer, stabilizers down, trailer as rigid as a house on foundations, then the choices are more restrictive.

If you don't mind the back hanging out over behind the pad, maybe not able to use the stabilisers & are content with a little jiggle when you walk, then your options are greater.

This person's youtube post might help you.
Camper Report

A good source for information w.r.t. typical spur lengths in the National Forests is ForestCamping.com. That will definitely get you started.

The short answer is yes, size matters. A step further, the larger it is the more size matters. Some states & their SPs are notorious for small sites. Others can handle rigs up to the mid 30s without much trouble. Most COE or former COE CGs are great. The private CGs will cram you in one way or another.

I sure would not buy a rig based on the limitations of one state, even if it were my home state.

Durb's advice is darned good. Me too.

We are 33’ long and have had some tight spots but never couldn’t get in.

We have a 32’ travel trailer and often stay in state, national, and COE campgrounds. The only national park we visited, where you may have an issue is Mt. Rainier. We have fit in all of the other parks we have visited. We spent 8 weeks in CO and Utah this fall and stayed in many national and state parks.

Our trailer is 31 ft and we have no problems in OR and WA. However, we like full hook ups or at least water and electricity. Maybe the sites with those amenities are longer. We use Reserve America and find that their pad length descriptions are fairly accurate.

We do three month out West without reservations every other summer staying mainly in USFS CGs that do not take reservations. At 42' I'm SOL if I show up Friday but late Sunday or Monday, no problem. One of my favorite CGs in the Tetons says 28' max but I can get into three of the 12 sites...not sure who decides what lengths to post. CA is probably the worst for larger units, but you did not include it so I would go even bigger if that is what the DW wants.:B

Been to many state parks in Wa and Oregon and you will not have a problem with a 30 fter, we fulltime and been all over Oregon and Wash parks in a 39 fter and every once in a while a few of the parks are a little tight but you will be good F.Y.I. if staying at the Parks make reservations WAY in advance for the summertime or you will be camping in a Walmart parking lot;)