Once you get to the Recreation.gov site and look up your trailhead, you may see "W", which indicates that walkup permits will be available (but are not available yet). So the trick is that these become available 2 weeks in advance. So what you want to do is to log in to recreation.gov at 7 AM 2 weeks in advance of your intended data and try to grab any walkup permits that became available.
Note that recreation.gov works on "Eastern Time" and the release actually happens at 10 AM EST (which is 7AM in Tucson or in the Pacific -- at least in the summer when daylight savings time is active in the rest of the nation. Also note that when I check on Friday 6/18, I see that permits have opened up for Friday 7/2 -- so the "2 weeks" means 13 days not 14 days. So if you want a permit for Monday July 19, be checking on 7 AM Monday July 5.
I'll also note that this used to be only half of the process. You get a reservation, but your permit gets delivered as a separate thing later. On one trip in 2020, I had a reservation, but my permit had not yet arrived. I took the reservation (which they clearly indicate is NOT a permit) hoping to negotiate with any ranger I encountered. I never encountered any. Once I got home, I discovered that the permit had arrived the day I set foot on the trail. I had left my home in Tucson the day before the permit arrived and there was no possible way I could have printed it and carried it with me. I have no idea if this mess has been fixed this year
Permits are a fact of life if you want to hike in the Sierra. There is a quota system (summer and fall, i.e. May 1 thru Nov 1). 25-40 percent of permits are reserved for walk in on the day they are issued. The rest are reservable in advance for a $5 per person fee (non refundable). (but see below for some additional fees they now are tacking on). Also the rules are always changing, so check the official agency web pages for details that I am not staying on top of.
Note that there are multiple agencies you may find yourself dealing with. Most of my experience has been with the Inyo National Forest. However, the agency that issues the permit is the agency within which your hike starts. So, if you are starting a hike in Yosemite park, you will be dealing with the parks permit reservation system, which as of 2013 is not recreation.gov, as it now is for the Inyo Forest.
Unless you plan to exit at Whitney Portal, they only care about your entry date (though they do ask how many nights you expect to be in the backcountry and try to get some idea of your itinerary, either for statistics gathering or so they have a clue if they need to launch a rescue, who knows.) You must pick up your permit by 10 AM on the day it is issued for (or call them if you are running late - good luck with that!) otherwise it will be released to walk-in people for that day.
Everything changed in 2012 as they switched to a long promised online reservation system for wilderness permits. To use the new system (for Inyo Forest only) you go to:
It is awkward and clumsy, but gets the job done. Once there, you can fumble around like I did. and select "Inyo" and "wilderness" What seems to work is to search for "Inyo National Forest Wilderness Permits". Hopefully that will get you started. It is a good example of how not to design a web site. Good luck, you will need it.
There is a $5.00 per person fee, and also an irksome $6.00 "reservation fee", so it cost me $11.00 to make a reservation for one person in June of 2012.
The following list of links and phone numbers were once helpful in planning and arranging trips, and perhaps still may be. It is challenging and difficult to get up to date trail information (from the government web sites anyway). In May of 2011, the Whitney Ranger station phone system was still playing a message describing Mount Whitney trail conditions in Ocober of 2010, with the admonition that "winter was on its way!!". Government agencies, in their effort to "look busy" are always rearranging their web pages, with little if any addition (and sometimes subtraction!) of content. I suppose this allows them to boast on annual reports of updating their web pages. I used to keep shortcuts here to key sections of their web pages, but have abandoned that as a hopeless endeavor.
I will say this for them, as wretched as their phone system and internet pages are, most of the human beings that I have had occasion to talk to have mostly been quite nice and helpful.
Once you have a reservation, you still need to go to an Inyo Forest Ranger station (there are four). It doesn't matter which one, any of them from Lone Pine to Lee Vining can write a permit. This proves to be a pain in the butt, since I find myself hard pressed to make the drive from Arizona and get there before they close for the day. As a result, I camp somewhere, get the permit in the morning, and drive to the trailhead and begin hiking mid-morning, rather than the crack of dawn. I suppose the main point of this is that you can be informed of rules and regulations, (which you can read on the website or the stuff they mail you with the reservation paperwork). I wish they would just mail the permits -- maybe this also helps them to confirm who actually shows up and gets on the trail, thus allowing them to allocate walk-in permits.
They mention a night box on the website, but told me in 2009 that this cannot be used if your trip will enter SEKI park. Maybe this has changed.
You can pick up your permit a day or two before your entry date. You must pick up your permit by 10AM, or your permit may be given to a walk-in person.
Taboose and Sawmill pass have a quota of 10 people per day. 6 permits may be reserved ahead of time, the other 4 are available for those who walk in the day of the permit. Baxter allows 8 people (split 5/3) and Shepherd Pass allows 15 (split 9/6). North Fork of Lone Pine Creek allows 10 (split 6/4).
Tom's hiking pages / tom@mmto.org