Stacey Lovewell's 2-year-old granddaughter spotted the rock first, as she climbed inside one of the giant Os that spell out "ZOO" along Capitol Parkway, near the Lincoln Children's Zoo.
The small stone was painted purple, with a picture of a tree and the name of a Facebook group on the back: "SE Nebraska Rocks."
"Oh, my gosh, this is so cool," Lovewell remembers thinking.
She had stumbled upon a national trend that started two years ago with a woman in Massachusetts and only recently took root in the Midwest.
In the past six months, thousands of Nebraskans have joined Facebook groups dedicated to painting and hiding rocks.
They cover the stones with colorful images or inspiring messages, then hide them at parks or outside stores — just about anywhere strangers are likely to find them.
"Hopefully it brings a smile to their face and a little bright spot to their day," Lovewell says.
But the craze isn't catching on with state and Lincoln parks officials.
The Nebraska Game and Parks Commission has asked visitors to refrain from hiding painted rocks in state parks and recreation areas, saying it violates a regulation against disturbing the natural landscape.
For many visitors, encountering painted rocks "diminishes the land's beauty and the experience of being in nature," state parks administrator Jim Swenson said in a news release Wednesday.
Other state and national parks across the country have also asked guests not to hide painted rocks, Game and Parks says. So have staff at Pioneers Park Nature Center in Lincoln.
Lincoln Parks and Recreation Department guidelines adopted in 2004 prohibit people from burying geocaches — hidden items intended to be found by others using GPS — at city parks, or placing them anywhere at Pioneers Park Nature Center, Sunken Gardens or Hamann Rose Garden at Antelope Park.
The same rules apply to painted rocks, said Kat Scholl, a Parks Department spokesman.
Painted rocks could present a safety hazard for park workers — if one is kicked up by a lawn mower, for example, Scholl said. The brightly colored rocks can also interfere with sensitive ecosystems and animals.
It's unclear whether people who leave painted rocks at parks can be fined, but parks staff may remove any offending rocks.
"It's just kind of frowned upon," Scholl said.
Lovewell called the rules "disheartening."
She has painted more than 300 rocks since March, going through six 30-pound boxes she ordered from Walmart.
"We spend hours — hours — painting," she said. "The only reason that I'm doing it is to brighten someone else's day. I get great joy from the time that I spend creating.
"I'm not artistic. I mean, some of the rocks that I've put out look like a 5-year-old painted them, and I'm OK with that."
She understands that some people wouldn't enjoy finding the rocks, and that their bright colors aren't part of the natural landscape, but it saddens her to think that well-meaning creations might be tossed out with the garbage.
Lovewell, an in-home care nurse who lives in Norfolk, has left the rocks all over northeast Nebraska, including Columbus, Fullerton, Genoa and Monroe. Her daughter brought some back to Lincoln.
"I carry them in my purse. I have a backpack in my car that has more of them," Lovewell said. "We took a few to the state fair."
The northeast Nebraska rocks page she started in May has received comments from people across the country who happily post about finding the rocks.
"It's like the perfect rock shows up with the perfect person," Lovewell said. "The whole goal is to brighten someone's day."