But if the weather matches the July 4th weekend forecast, park managers know there likely will be thousands of folks left on the outside, looking in.
Last year, parks filled to capacity, when every parking space is taken, 54 times. Sandy Point, just north of the Bay Bridge, was at capacity six days, three of them coming during the long Independence Day weekend. Manager Ken Hartman anticipates a repeat performance.
"We have people waiting at the gates at 6 a.m. Regulars know what picnic tables they want and what grill they want and they stake them out," Hartman says. "When our lots are full, we have 7,000 to 8,000 people in the park and that's our limit."
The same is true at Greenbrier, south of Hagerstown, which reached capacity 19 times last year and this year began turning away cars on Memorial Day at 8:30 a.m.
"It's the busiest day of the year," says manager Dan Spedden of July 4 th. "If we were in retail, it would be Black Friday or Christmas Eve. You'd better be here at 5 a.m. or you won't get in. If we fill by 9, we'll spend the next six hours turning away about 1,000 cars."
The park service is working on a text messaging system that will tell subscribers when the 66 parks are full, but officials don't want to roll it out until they are sure it can deliver a timely warning.
Instead, they are passing along a simple message this weekend, says Superintendent Nita Settina: "Come Early and Come Together."
Last year and during Memorial Day weekend this year, families arriving in separate vehicles at different times had their plans upset when parks closed before everyone got inside.
"That happens a lot," says Hartman. "As we're turning cars away, somebody says, 'But my family is in there and I have all the food.' There's nothing we can do."
Spedden continues, "Or they think they'll use an advance team to get in early and grab a couple of tables before calling the others to come. But it doesn't work that way. The best thing is to come in a car caravan."
Families hoping to camp at a state park this weekend are likely to be disappointed. A few campsites are still available at Martinak State Park. Otherwise, the bulk of the 2,100 state park campsites and cabins are booked, says Barbara Knisely, chief of customer relations.
Parks with beaches — Gunpowder Falls, Sandy Point, Cunningham Falls and Greenbrier — fill up first, east to west. Rangers position themselves at access roads to wave off new arrivals, and staff at Rocky Gap say they can predict when the wave of visitors will reach them just by listening to the radio chatter about closures.
For safety reasons, state parks don't allow people to stay in line and wait for someone to leave, and at Sandy Point, visitors can't park elsewhere (if they could find an elsewhere) and walk in. Still, Hartman says, within minutes of reopening the gates, traffic forms a double line that runs back toward U.S. 50.
"I don't know where they hide," he says, laughing.
The pressure to reach water — any water — has more and more park visitors turning to river access to wade and swim, says Major Daryl Anthony, the central regional manager who oversees 11 parks.
"The 1930s pictures of Patapsco Valley show people pushing up their pant legs and skirts to go wading in the river to cool off and relax. People now are rediscovering it on their own. That's why North Point will fill to capacity July 4 and the Avalon area of Patapsco Valley has picked up. It's 100 percent word of mouth," Anthony says.
Park managers say generally speaking Saturday is the least busy of the three days, and if you can't get there by mid-morning, try later in the afternoon, when some visitors have had their fill of sun and fun and begin to pack up. Anthony says the parks closest to Baltimore tend to fill later because people make a last-minute decision, often based on the weather.
If your first choice is one of the busiest day-use parks, you might want to have a back-up in mind, Settina says.
Fireworks are not permitted in state parks, and since day-use areas close at sunset, visitors shouldn't expect to use a park as a viewing area for nearby municipal displays.
Finally, says Hartman, "If you're not going to get here at 6 a.m., bring a grill because our supply is limited and they get snatched up right away. And bring everything you need, have all your supplies, because if you leave the park and we close, you can't get back in."
Six alternatives to the most popular parks
Seneca Creek: The Montgomery County park has a lake and rental boats, a nature center, plenty of shade and fishing.
Patapsco Valley: McKeldin area. You can rock hop and wade in the upper river in a lesser-known portion of the park.
Elk Neck: The Cecil County park has a wading beach (no lifeguard) and a lighthouse.
Calvert Cliffs: A 1.7-mile walk to a sandy beach with views of 100-foot cliffs and plenty of fossil hunting.
Rocks: Harford County park has tubing, fishing and paddling in Deer Creek.
Tuckahoe: Rent a canoe or kayak, go fishing, picnic under the pine in the Queen Anne's County park.Copyright © 2015, The Baltimore Sun