How do I solve 4 down in Daily Telegraph Cryptic 3373?

Question

Accepted Answer

4 down reads "Gather in a US state" (5 letters); the answer is AMASS. It's a charade: the answer breaks into parts in clue order, each part clued by a word or short phrase. No indicators needed; watch for standard abbreviations (RA = artist, US = American, IN = at home) and short synonyms. The full step-by-step breakdown is on this page.

Gather in a US state (5)

4D — Gather in a US state (5) — AMASS