You might not even realize that the poem is "set" in a place called Lagunitas if not for the title. For a pastoral poem, there’s not that much nature imagery from the place that he praises. After the image of the woodpecker pecking away at a black birch, the poem shifts away from the present moment at Lagunitas, and heads into the past. But, Hass wants to argue that the past is a big part of the present.
If you put two mirrors across from one another and look into one of them, you’ll see the same image reflected over and over again from further and further away. The reflections seem to go on into infinity. "Meditation" is like one of those images, reflecting the present moment, but going further and further into the past to discover the source of its mystery. First, we get the immediate past – the night before – when the speaker talks with his friend. Then, he remembers a woman whom he makes love to, which in turn reminds him of fishing on a riverbank as a child. All of these images are connected by the speaker’s memory.
Even as he looks at the woodpecker and thinks about philosophy, his mind already races back into the past with these associations. We always see the world filtered through our experience. So, the setting of this poem is kind of a mind-bender. It’s like we’re seeing five things at once in different distances from the present. If the speaker didn’t shift away from these images at the very end of the poem, you get the sense that he can provide even more connections with the past. That’s why he calls the distances "endless," as if they really do go into infinity. And, if you haven’t seen that trick with two mirrors, check it out: it’s a total trip.