From the SEKI wilderness permit website: https://www.nps.gov/seki/planyourvisit/wilderness_permits.htm:
Walk Up Wilderness Permits (Quota Season)
Step 1: Plan Your Trip
Decide where you want to go by looking at Trail Descriptions, the Park Atlas and Trail Conditions. Find the name of and quota limit for your desired trailhead on the Wilderness Trip Planner, entry quota map, or at Recreation.gov.
Step 2: Permit Issuance and Payment
Walk-up permits can be obtained starting from 1:00pm the day before your trip begins. Permits are only issued?during hours of operation by trailhead rangers who provide important area information.
You must arrive at the correct trailhead desk for the trailhead you are hoping to obtain a walk up permit for. Bring your entire party to the orientation.
You will pay the fee of $15 per permit plus $5 per person at the issuing station. Credit cards are the preferred payment method. Trailhead rangers will not be able to make change for transactions.
On your desired entrance date, once all of the quota for walk up permits is taken, a list will be started for permits that become available if a reserved party does not show up by the 10:00 am deadline. These no-show permits will become available for first-come first-serve walk ups.
different locations/jurisdictions have different permit policies. Using the wayback machine online I looked at the page for 2019 and that was prior to them using recreation.gov (they still had permit applications you had to email as an attachment) it appears that the current process for walkups being in person only for SEKI was in place in at least since 2021 when things fully reopened after covid based on looking at a handful of website captures there.
