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State and national parks believe they have gained the upper hand in a war against software bots that monopolize campground and trailhead reservations.

As the reservation season gets underway — with key reservations dates imminent the morning of Jan. 2 for Fourth of July weekend at state parks, Point Reyes National Seashore and marque sites at lakes on national forest land — authorities are hoping to level the playing field.

On Oct. 1, federal officials unveiled an overhaul to Recreation.gov, the reservation service for national parks and national forest nationwide, as well as for trailhead permits for Half Dome and Mount Whitney. The system requires each user to start fresh and sign in with a new password, which operators say allows them verify and identify each as a real person. They hope that translates to no more tech wizards using bots to game the system.

At the same time, the state parks reservation system, ReserveCalifornia, made the same changes, as well as a few others, to fight software bots.

“Our new system has security features installed to reduce the opportunities for bots to access reservations, broader search functions and also limits the number of modifications a reservation holder can make,” said Jorge Moreno at State Park headquarters in Sacramento.

The problem was simple and inescapable: Campsites at many marquee state parks, such as Sunset on Monterey Bay, were listed as booked full, day-after-day. But upon inspection, authorities often revealed unoccupied campsites, to the chagrin of many. In an extreme case, rangers at Yosemite National Park tracked an encounter where Half Dome climbing permits were being resold on Craigslist, according to park headquarters.

As a result, reservation services, with oversight from state and national parks and the U.S. Forest Service, overhauled their systems and protocols for this winter. In addition, both state and national parks have banned the re-sale of reservations.

As part of its overhaul, reservation service ReserveCalifornia.com added an additional twist — a new “rolling window” to reserve dates for state park sites. A rolling window means the exact date, six months out, is available each ensuing day. That tweak ends the first-of-the-month crush when dates for an entire month became available at a single moment, such as when the clock ticked 8 a.m. at Jan. 2 for dates six months out in July.

Each month, thousands competed in a monthly scramble when they tried to book campsites online. Many of the more popular sites sold out for an entire month within hours. That has been fixed, Moreno believes.

The reservation services have been enhanced to show dates that are booked by site, as well as next date a site is available. This allows campers to plan well ahead. In addition, a new system to reserve trail camps in the Santa Cruz Mountain includes a calendar that shows availability by site and date, and a page on the website with a map that shows the location of trail camps to plan multi-day trips, where you could hike from camp to camp.

In the big picture, well-known campsites at world-renowned destinations fill quickly. But California has roughly 1,600 campgrounds, including about 750 campgrounds at lakes, streams and trailheads across 20 million acres of national forest; you can make reservations at about half, and the rest are off the grid and are first-come, first-served. Those who know all the choices never get stuck.

If you want to camp this summer in Yosemite Valley, Point Reyes National Seashore, Angel Island State Park, along Monterey Bay, climb Half Dome or Mount Whitney, or hike the John Muir Trail from Whitney to Yosemite Valley, then you have no choice: You must play the game.

State Parks

Target dates: 8 a.m., Jan. 2 for all dates through July 2, where you can extend your booking through Fourth of July weekend. Other key dates: New rolling service means arrival dates are available six months to day from booking date; Feb. 1 for August 1, March 1 for Sept. 1, where you can extend through Labor Day Weekend. Reserve at www.ReserveCalifornia.com or 800-444-7275 (discouraged, long wait times common).

Most in demand: Steep Ravine Cabins; New Brighton, Seacliff and Sunset State Beaches on Monterey Bay; Angel Island; Samuel P. Taylor; D.L. Bliss.

Least in demand: Mount Diablo State Park, Henry. W. Coe.

Note: The Redwood Empire has more than 10 campgrounds where all rarely fill at the same time; of these, Prairie Creek, Jedediah Smith and Patrick’s Point are the most popular.

Contact: California State Parks, www.parks.ca.gov.

Point Reyes trail camps

Target date: 7 a.m. Jan. 2 for all dates through July 2, where you can extend through 4th of July weekend. Arrival date may be reserved six months ahead to the day. Other target dates: Feb. 1 for August 1, March 1 for Sept. 1, where you can extend through Labor Day Weekend. Reserve at www.Recreation.gov.

Most in demand: Wildcat, Sky.

Least in demand: Glen, Coast, Tomales Bay boat-in.

Note: Two great routes for backpacking: Coast Trail to Palomarin, 16.1 miles one-way, with camps at Coast and Wildcat; or Sky Trail to Palomarin, 15.3 miles, one-way, with camps at Sky and Wildcat.

Yosemite National Park

Target dates: 7 a.m. Jan. 15 for arrival dates May 15 through June 14, including Memorial Day Weekend. Other key dates: Feb. 15 for arrival dates June 15 through July 14, including 4th of July Weekend; March 15 for arrival dates July 15 through Aug. 14; April 15 for arrival dates Aug. 15 through Sept. 14, including Labor Day Weekend. Reserve at www.recreation.gov.

Most in demand: Upper Pines, Lower Pines, North Pines in Yosemite Valley; Tuolumne Meadows, White Wolf along Tioga Road.

Least in demand: Wawona, Bridalveil, Yosemite Creek, Porcupine Pine Flat.

Note: All campgrounds in Yosemite Valley fill from late April through October. The best opportunities are season openers in the high country at Yosemite Creek, Bridalveil.

Santa Cruz Mountains

Target dates: Reservations available up to 60 days in advance. For instance, Jan. 20 for dates during peak waterfall flows on March 20; or March 1 for May 1, when weather typically warms.

Most in demand: Sunset, Castle Rock, Twin Redwoods.

Least in demand: Waterman Gap, Jay, Slate Creek, Butano Trail.

Note: 52 sites available at 7 trail camps. The reopening of minimum-impact camping in winter in the Santa Cruz Mountains means you could complete the Skyline-to-the-Sea Trail, Castle Rock through Big Basin to Rancho del Oso, when the waterfalls are at peak flow. Present route with a bypass is about 36 miles, where you would camp at Waterman Gap, Jay Camp and then out (three days, two nights, with shuttle vehicle); minimum impact means you provide your own water (from creeks) and pack out all trash, including toilet paper.

Contact: Santa Cruz Mountain Trail Camp page, www.parks.ca.gov/?page_id=26658; more info c/o Big Basin Redwoods State Park, 831-338-8861.

Lakes in U.S. National Forest

Target date: 7 a.m. Jan. 2 for all dates through July 2, where you can extend through 4th of July weekend. Arrival date may be reserved six months ahead to the day. Other target dates: Feb. 1 for August 1, March 1 for Sept. 1, where you can extend through Labor Day Weekend. Reserve at www.Recreation.gov.

Most in demand: Three-day weekends at Shasta Lake, Lake Tahoe, Bowman Lake Rec Area and similar.

Least in demand: Small lakes reached with 4x4 near Bucks Lake region, Trinity-Divide, Carson Pass.

Half Dome

Lottery target dates: Deadline for applications March 31, available for submission March 1; lottery results announced in mid-April.

Note: 225 permits are available by lottery for each climbing day. Success rate is better than 50-50 for those applying for weekday permits, rangers say, and about 1-in-4 for weekend dates. The tentative plan for 2019 is to put up the cables on the backside of Half Dome on May 24 and be available through Oct. 15.

Contacts: Lottery application at www.recreation.gov; info at Yosemite National Park, www.nps.gov/yosemite.

Mount Whitney/John Muir Trail

Lottery target date: Deadline for applications is March 15, and available for submission Feb. 1; lottery results announced on March 24. Any remaining permits will be sold on April 1.

Note: Permits will be awarded to 100 hikers and 60 backpackers per day. Odds are roughly 1 percent of application being drawn.

Contacts: Lottery application at www.recreation.gov; info at Mount Whitney Interagency Visitor Center, 760-876-6200, www.fs.usda.gov/inyo.

Tom Stienstra is The Chronicle’s outdoor writer and the author of Moon California Camping. Email: tstienstra@sfchronicle.com. Twitter: @StienstraTom. Facebook: www.facebook.com/tomstienstraoutdoors.