Three short tercets and a stretch of chatty prose make an odd pairing, and the poem works because of the gap between them. The verse is hushed and exact. The note at the end is plain, funny, and a little embarrassed. Together they say something true about how we look at the places we live in: we assume we know them, and then something small shows us we don't.
The first tercet begins with a huge span of time: "ancient seabed." Without a verb, the phrase just sits there like a rock face. Then comes "a sudden roar / from the quarry," which drags us into the present. The poem doesn't say how the two are connected, but the judgment is easy to make: a quarry cuts into old ground, and the speaker seems to be standing somewhere where the land itself is a record of vanished water. The sounds help. The soft, hissing "s" of "ancient seabed" and "sudden" gives way to the growling "r" of "roar" and "quarry," so the stanza gets louder as it goes.
The second tercet turns the roar into something more ambiguous. "Higher pitched / than my memory / first cicada" can be read two ways, because there is no punctuation and the line breaks do the work. It might mean "higher pitched than my memory [of the] first cicada." It might also mean "my memory's first cicada," as though the insect were the opening item in a mental list. Either way, the sound is not what the speaker remembered. The cicada's shrill whine has been stored in the mind at the wrong pitch, which is a quiet admission that memory flattens and softens the world. The roar of the previous stanza may even be the cicada itself, loud enough to sound like machinery. The poem lets that stay uncertain.
The third tercet moves from season to hour. A gnomon is the part of a sundial that casts the shadow, and the question "which tree / will be today's gnomon" turns the whole woodland into a clock where any trunk might do the job. The word has a silent "g," and the last line, "great grey slug," answers it with a heavy, chewy run of hard g's. After the grand word comes a soft, slow, slightly ridiculous creature. Nothing in the tercets has a regular rhyme or meter, and the lines are short, mostly two to four syllables. That keeps the reader's eye moving downward at the pace of someone walking and stopping, walking and stopping.
Then the prose arrives. "I just found these coral fungi less than 50 feet from my front porch." The detail that matters here is "coral." The poem began with an ancient seabed, and now a fungus named after sea creatures turns up on dry land. The connection is never pointed out, but it makes the opening feel less random. The numbers also set up a contrast with the first stanza. Millions of years, if we read "ancient" that way, have shrunk to fifty feet.
The speaker's question, "Why don't I ever go back here?", is the sort of thing you say aloud to yourself, and "I muttered" confirms it. The answer comes through a change of posture. Crouched down to take a photograph, he sees only the fungi. Standing up, he sees the whole patch: "all the poison ivy. That'd be the reason." The contraction and the flat, deadpan sentence show a poem choosing humor over a tidy moral. Close attention gives wonder, and a wider view gives a warning.
That is what makes the poem worth reading. It would be easy to end on the cicada, the shadow, and the slug, and let nature seem like a calm lesson in time. Instead the poem admits that nature is also itchy, that we avoid parts of our own yards for good reasons, and that attention comes with a price. The note's honesty makes the earlier tercets more believable. A speaker who can laugh at his own neglect has earned the right to be amazed.