Archaeology: reconstruct deposition before dating behavior

Predict

Before calculating or reading feedback, predict what the evidence can establish and name one competing explanation.

An object can be older than the deposit containing it. A later disturbance can also move an object into an earlier layer. Archaeological inference therefore requires a formation history before a cultural interpretation.

Inspect the authentic source

The NPS distinguishes chronological, historical, cultural, social and geographic contexts. It describes archaeological context through associations among artifacts, ecofacts and sites, and emphasizes documentation of those relationships.

Source: National Park Service. Date: 9 May 2023. This source note is an authored paraphrase.

Worked analysis

Synthetic desk excavation: layer A lies above B. B contains a coin first minted in 1880 and worn pottery with an earlier style. If B is an undisturbed deposit and the coin belongs to it, deposition cannot precede 1880; pottery age does not make B earlier. Now reveal a root channel connecting A to the coin’s location. Intrusion becomes a competing explanation, so the coin no longer securely dates all of B.

Build and challenge your account

Manufactured, deposited, recovered: three different dates

A fictional exhibit label dates the burial of a bottle to the end of its manufacturing range. Test that inference using a real museum's object descriptions and a separate invented formation record. All work is documentary; do not collect, excavate or disturb objects.

Inspect the authentic NPS object records

Golden Gate National Recreation Area's archaeological finds exhibit, sections “Dairy History,” “Mugs on the Beach” and “Anomaly?”, checked29 October2026. The table paraphrases selected catalog facts. The bottle range is the NPS attribution from a manufacturing mark; the mugs' range is the named maker's operating period. Neither is a recorded disposal date.

The exhibit places these objects at three different locations. Displaying them together does not establish one buried assemblage, a shared depositor or a single event. The spoon has no maker's marks; missing production information remains unknown. The mugs' reported discovery in the1940s and receipt in1999 describe different events. No images or restricted collection details are reproduced.

Selected authentic descriptions; not a single deposit

ID / object	Location	Production evidence	Discovery	Receipt	Exact deposition
BOTTLE: United Milk / Bossy Brand bottle	Sutro Heights	1910–1940, NPS method attribution	1981, construction work	Not stated	Not supplied
MUGS: Two fused Greenwood China mugs	Fort Baker beach	1890–1929, maker operating interval	1940s, reported discovery	1999, turned in to park	Not supplied
SPOON: Unmarked thin metal spoon	Alcatraz tide pool	Unknown	1981	Not stated	Not supplied

Write one sentence correcting “manufactured by1940 means buried by1940.” An object can remain in use, be stored or be moved after manufacturing stops. The catalog alone does not choose among those histories or date a site's first occupation.

Initial exhibit correction and one alternative historyCapture correction and settings

Separate fictional transfer: a deposit with two objects

Invented object A was manufactured sometime1810–1840 and securely belongs to the original deposit. Object B was manufactured sometime1850–1860. These are exact stipulated ranges for this exercise, not the Golden Gate objects. “Secure” below means evidence establishes B as part of the original deposition, not merely found nearby.

NPS dating-method guidance, updated9 May2023, describes a terminus post quem: an earliest possible deposition bound from securely associated dated material. For this exercise, deposition cannot precede the latest secure production start. A separate, independently dated intact seal can provide an upper bound. All dates here have year-level precision; the seal states the deposit was already present by that year.

Association of object BSecure original associationDocumented later intrusion: exclude B from original depositAssociation unresolved: do not assume B is original Independent sealing recordDeposit already present by1870Contrary record: deposit already present by1830No independent upper-bound record

Supported lower bound: 1850. Independent upper bound: 1870.

Compatible years under the stipulated records: 1850 through 1870. This is a logical range, not a confidence interval or a uniform probability distribution.

Exact deposition year and beginning of occupation remain unknown. Removing a suspicious object can widen the range; a contradiction requires investigation, not a forced date. Test the1830 seal with secure B, then with documented intrusion, and explain why only one configuration has compatible years.

Compare formation histories and revise your exhibit

With both objects securely original, the later starting manufacture range gives1850, not1860, as the lower bound. The independent1870 seal gives1850–1870. Documented intrusion excludes B from dating the original deposit, leaving1810–1870. Without a seal, the end of manufacture does not supply an upper bound. Secure B plus the1830 seal is inconsistent.

The actual NPS objects come from different places and do not inherit any of these fictional constraints. Correct the original label using object IDs; distinguish manufacturer attribution, discovery and museum receipt. Request field notes and association records before proposing a shared deposit or a depositor's identity. A style or maker alone cannot identify a whole community.

Revised exhibit label, contrary history and records needed

Copy your chronology report

Read-only JSON report{ "sources": [ "https://www.nps.gov/goga/learn/historyculture/archeological-finds-at-golden-gate-national-recreation-area.htm", "https://www.nps.gov/articles/000/how-do-archeologists-date-sites-and-artifacts.htm" ], "historicalObjects": [ { "id": "BOTTLE", "object": "United Milk / Bossy Brand bottle", "location": "Sutro Heights", "production": "1910–1940, NPS method attribution", "found": "1981, construction work", "received": "Not stated", "depositDate": null }, { "id": "MUGS", "object": "Two fused Greenwood China mugs", "location": "Fort Baker beach", "production": "1890–1929, maker operating interval", "found": "1940s, reported discovery", "received": "1999, turned in to park", "depositDate": null }, { "id": "SPOON", "object": "Unmarked thin metal spoon", "location": "Alcatraz tide pool", "production": "Unknown", "found": "1981", "received": "Not stated", "depositDate": null } ], "audit": { "fictional": true, "association": "secure", "seal": "1870", "productionA": [ 1810, 1840 ], "productionB": [ 1850, 1860 ], "lower": 1850, "upper": 1870, "conflict": false, "interval": { "from": 1850, "through": 1870 }, "conditionalLowerIfBOriginal": null, "exactDepositDate": null, "occupationStart": null, "oneHistoricalAssemblageEstablished": false }, "worksheet": { "draft": "", "captured": null, "revision": "" }, "feedbackSeen": false, "temporary": true, "masteryAssessed": false }

Reset chronology worksheet

Feedback opened this visit: no. Reset clears writing and restores secure B/1870 seal; exposure remains until reload. Copy temporary work before leaving. No archaeological interpretation or mastery is automatically certified.

The published museum records and separate numerical transfer extend the opening fictional coin example. Do not treat objects from different locations as one context.

Draw a cross-section and two event sequences, one with an intact deposit and one with intrusion. Separate object manufacture, use, discard and burial. State exactly which association supports each inference, then identify the field record that would help distinguish the sequences.

Use a separate line for each conclusion. Beside it, identify the source record, transformation or interpretive step, and assumption that could fail. Keep observations separate from explanations. If two interpretations fit the same record, identify an additional observation that would distinguish them rather than choosing the more familiar story.

Independent transfer

A museum object has a date but no recorded find location. Which claim needs the greatest caution?

Write an answer before opening feedback. State what changes in the new setting and which part of the original reasoning still applies. A good transfer answer includes both a useful inference and a boundary on that inference.

Limits

This is a paper reconstruction, not instructions to excavate or collect. Context includes community knowledge and ethical stewardship. Manufacturing dates, styles and deposits have different uncertainties; no single object identifies an entire culture.

Review your evidence

Check the units and denominator of every number; check the author, date and access of every account. Distinguish an absent observation from evidence that an event did not occur. Retain a short revision note so a reviewer can follow how your conclusion changed.

Extend

High school: Produce the specified table, timeline or diagram; cite the source record and mark assumptions. Explain one tempting but unsupported conclusion.

AP-connected practice: Use this as interdisciplinary evidence practice where relevant to an existing AP course. Write a claim with specific evidence and a counter-explanation. This family is not represented as a separate AP course.

College: Extend the mechanism with a second authentic record selected for its ability to challenge your interpretation. Document sampling, measurement or source-access limits and a reproducible analysis trail.