A queen mattress is about sixty inches by eighty and will not hold a rigid shape. A Santa Monica walk-up typically gives you a bedroom door, a short internal hall, a unit door that opens inward, an external stair with a landing barely deeper than the door swing, a courtyard path and then the alley. That is five direction changes, and the binding one is almost always the landing rather than the stair itself. Memory foam makes it worse, not better, because it sags through the middle exactly when you need it to behave like a board.
The tuck-under and subterranean garages common north of Wilshire and through Ocean Park add a different problem. They are the natural route to the alley, but the posted clearance is low and a box truck cannot follow, so the mattress comes out through the garage on foot and meets the vehicle at the street or the alley mouth. That is fine when it is planned and awkward when it is discovered.
The alley itself deserves respect. Santa Monica's residential blocks are alley-served, which is genuinely convenient: it is where the bins live, where the garages open and where the city asks you to put bulky items. It is also narrow, shared, and the only vehicular access to a row of garages. A mattress left across it for ten days is not a small inconvenience to one neighbor, it is the access route for the block. We stage in the alley only as long as it takes to load.
Then there is the building's own layer: notice for a move, elevator padding in the midrise stock, a designated loading door, and in many managed buildings a certificate of insurance before a crew works in the building. All ordinary, all much easier the day before. And one Santa Monica specific: on multiple-unit turnovers, which are common here, the labor per mattress falls sharply once the route is set up, so doing six at once is far more efficient than doing one six times.
Finally, the marine layer. Santa Monica sits on the coast and mornings are damp for much of the year. A mattress bagged at the door and loaded straight onto a truck is dry. One that has waited in an alley through a week of marine mornings is not, and dampness is the main reason a mattress gets downgraded at a processor. If the mattress is part of a larger clearance see furniture removal in Santa Monica.