Tanja and I climb on rocks at the far end of Emigrant, at the end of a trail we’ve only just discovered. It follows the new, high edge of the water.

The boulders are car-sized and round as the curves on a teddy bear. I reach the top first, followed by my sister, then Penny, who sniffs the air knowingly.

“What are those?” she asks, pointing to the dark shapes in the sky below us, all wing, rising and falling with the lake thermals.

“Turkey vultures,” I tell her, my big-sister, teachable-moment voice coming out unintentionally. It’s a reminder of our difference: up until this spring, she’s been a stay-in kind of kid. All along our hike, golden-headed mushrooms, the articulate red branches of manzanita, even poison oak have been new friends — and enemies — she’s never been formerly introduced to. I turn and squeeze her arm.

“I’m so glad we’re having more adventures together these days.” Now I sound like her dad, but it needed to be said, even awkwardly.

To let her know we don’t have to talk about it, I look up toward the sky, my eternal mystery machine. In marveling, I notice a hint of rainbow surrounding the sun’s glare. I think it’s my sunglasses but Tanja sees it too. I take off the shades and cover the sun with my hand. True enough, a rainbow all around that burning orb, thin as the veil of water molecules hazing the blue.

Not my first solar rainbow, but hers.

“Why does that happen?” she asks.

I’m happy to say that I don’t know.