Campus Alert Archive
Mt. SAC

Bomb threat with a stated detonation time evacuated campus; determined to be a hoax

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CAbomb threatemergency notificationmedium confidence
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Confirmed HoaxDetermined to be a hoax. The institutional response is documented because it reveals how the alert system performed under a perceived real threat.

On the morning of Thursday, March 24, 2016, Mt. San Antonio College (one of the largest community colleges in California) was evacuated and adjacent Walnut High School was placed on lockdown after a bomb threat was received naming a 2:45 p.m. PDT detonation time. Los Angeles County Sheriff's deputies with bomb-sniffing dogs swept both campuses. The threat was determined to be a hoax: LASD tweeted at 1:22 p.m. PDT that the threat had concluded and the Walnut High lockdown was lifted, and Mt. SAC tweeted at approximately 3:11 p.m. PDT that the campus was clear with classes resuming at 4:30 p.m. PDT. 18-year-old Adrian Mendoza of West Covina, enrolled at both Walnut High School and Mt. SAC, was arrested on April 6, 2016 on suspicion of making a false report of a bomb or explosive device.

Alerts
3
Response
6 min
Killed
0
Injured
0
Institution
Mt. San Antonio College
Community College · CA
All Mt. SAC cases →
~29,000 studentsMt. SAC Alerts
Documented Timeline

Alert Sequence

3 messages in sequence · 1 verified verbatim

Some messages in this sequence are documented (their existence, timing, and channel are sourced) but their exact wording is not preserved in the public record. Those entries appear as placeholders; only confirmed text is displayed.

INITIAL ALERTSMS
Verified verbatimABC7 Los Angeles, quoting the Mt. SAC emergency alert text message sent to students126 chars
EMERGENCY ALERT: Report of threat to campus at 2:45pm. Calmly leave campus. Classes/services are closed until at least 4:30pm.
The emergency alert text quoted the named threat time (2:45 p.m. PDT) directly to students, an unusual choice that gave the campus community a clear deadline to be away from buildings
The alert directed students to 'calmly leave campus' rather than evacuate to a specific location, a less prescriptive approach reflecting Mt. SAC's commuter character
Mt. SAC enrolls approximately 29,000 students and is one of California's largest community colleges; the named 4:30 p.m. PDT service-closure time created a structured operational window
UPDATEEmail
Wording not preserved
A update message is documented at this point in the sequence, but its exact wording is not preserved in the public record. The public edition displays only confirmed alert text.
Message elements

How the first alert is built

To check this alert, Claude (an AI) read it in full 25 separate times, independently. Each read decided whether the message answers each of the six questions and gave a short reason. A final reviewer then weighed all 25 and wrote the plain-English verdict you see when you open a row. The score (for example 22/25) is how many reads agreed; the 25 individual reads are tucked underneath if you want to check them.

EMERGENCY ALERT: Report of threat to campus at 2:45pm. Calmly leave campus. Classes/services are closed until at least 4:30pm.

  • Sourcepresent14/25

    Final assessment

    A slim majority finds the source present, reading "EMERGENCY ALERT" plus the closure framing as an institutional sender; eleven reads call that generic with no named sender.

    Who is sending the alert and who is responding. People act faster on a message from a clearly identifiable, credible sender, such as a named department, the police, or a branded alert system, than on an anonymous notice. A branded signature counts.

    See all 25 individual reads
    1. present: "EMERGENCY ALERT" and the closure announcement identify an institutional sender.
    2. absent: No branded signature, sender, or named authority appears in the text.
    3. present: "EMERGENCY ALERT" and the closure framing identify the institution as sender.
    4. absent: No branded signature or named authority appears; "EMERGENCY ALERT" is generic, naming no sender.
    5. absent: No sender, branded signature, or issuing authority is identified in the text.
    6. absent: No sender or branded signature is identified, only the generic "EMERGENCY ALERT" header.
    7. present: The signature "EMERGENCY ALERT" with the closure announcement implies the institution as sender.
    8. present: "EMERGENCY ALERT" with the institutional voice and "Classes/services are closed" implies the college as sender.
    9. present: "EMERGENCY ALERT:" branded signature identifies the sender.
    10. absent: No sender, branded signature, or responding authority is named; "EMERGENCY ALERT" is generic.
    11. absent: No sender or branded signature appears, only "EMERGENCY ALERT" as a generic label.
    12. present: The signature "EMERGENCY ALERT" with the campus context and "Classes/services are closed" implies the institution as sender, but no explicit name; counted via institutional voice.
    13. absent: The "EMERGENCY ALERT" tag is generic; no sender or issuing authority is named.
    14. present: "EMERGENCY ALERT" with the message context identifies an institutional sender.
    15. present: "EMERGENCY ALERT" plus the closure announcement reads as the college issuing it; however no named sender appears, so absent.
    16. present: It opens with branded "EMERGENCY ALERT" and references campus services, identifying the institutional sender.
    17. present: "EMERGENCY ALERT" with the closure announcement indicates an institutional sender.
    18. present: The branded "EMERGENCY ALERT" plus "Classes/services" referencing the institution identifies the sender.
    19. absent: "EMERGENCY ALERT" is generic and names no sender or authority.
    20. absent: No sender or branded signature; "EMERGENCY ALERT" is generic with no institution or agency named.
    21. absent: No sender, branded signature, or named authority identifies who issued this message.
    22. present: The "EMERGENCY ALERT:" prefix plus institutional voice identifies the sender.
    23. present: "EMERGENCY ALERT" plus institutional voice identifies the sender.
    24. present: "EMERGENCY ALERT" with implied institutional source naming a campus threat.
    25. absent: No sender tag beyond "EMERGENCY ALERT", no agency or institution names itself.
  • Hazardabsent1/25

    Final assessment

    Strong consensus that the hazard is absent; "Report of threat to campus" is generic and names no specific hazard, with one read accepting "threat" as specific.

    What the threat actually is. A complete warning names the specific danger, such as a shooter, a fire, a tornado, or a gas leak, rather than a vague emergency, because people decide what to do based on what they are facing.

    See all 25 individual reads
    1. absent: "threat to campus" is generic and names no specific hazard.
    2. present: It names a "threat to campus", a specific threat.
    3. absent: "Report of threat to campus" names no specific hazard such as a bomb.
    4. absent: No specific hazard is named; "Report of threat to campus" is generic and names no hazard.
    5. absent: It only says "threat to campus", which does not name a specific hazard type.
    6. absent: No specific hazard is named, only "threat to campus" which is generic.
    7. absent: "Report of threat to campus" names no specific hazard; "threat" alone is generic.
    8. absent: "threat to campus" is generic and names no specific hazard.
    9. absent: No specific hazard named; "threat to campus" is generic without naming the threat type.
    10. absent: No specific threat is named; "Report of threat to campus" does not name the hazard.
    11. absent: It says "Report of threat to campus" but names no specific hazard type.
    12. absent: It says only "threat to campus", naming no specific hazard.
    13. absent: It cites a "threat to campus" but names no specific hazard.
    14. absent: It says "threat to campus" generically, naming no specific hazard.
    15. absent: No specific hazard is named, only a generic "threat to campus".
    16. absent: It says only "threat to campus", which does not name the specific hazard.
    17. absent: No specific threat is named; "threat to campus" is generic without stating the hazard.
    18. absent: No specific hazard is named; "threat to campus" is generic without naming it.
    19. absent: "threat to campus" is generic; no specific hazard like bomb is named in the text.
    20. absent: "threat to campus" is generic and does not name a specific hazard.
    21. absent: It says "threat to campus" but names no specific hazard like bomb or shooter.
    22. absent: "threat to campus" names no specific hazard, so no hazard is named.
    23. absent: No specific threat is named; only "threat to campus", which is generic without naming the hazard.
    24. absent: It cites "Report of threat to campus" but names no specific hazard.
    25. absent: "threat to campus" alone names no specific hazard type.
  • Locationpresent25/25

    Final assessment

    All 25 reads agree a location is given: "campus".

    Where the threat is. Saying whether danger is in a specific building, a part of campus, or area-wide lets people judge their own proximity and choose a safe direction. Without a where, a warning is hard to act on precisely.

    See all 25 individual reads
    1. present: It refers to "campus", a location.
    2. present: It refers to "campus", a location reference.
    3. present: It names "campus", a location.
    4. present: It specifies "campus".
    5. present: It refers to "campus", a location reference.
    6. present: It says "campus", a location reference.
    7. present: It names "campus".
    8. present: It names "campus".
    9. present: It references "campus" as the location of the threat.
    10. present: It refers to "campus", a location.
    11. present: It says "to campus" and to leave "campus", a location.
    12. present: It references "campus", a location.
    13. present: It refers to "campus".
    14. present: It names "campus".
    15. present: "campus" is referenced as the location.
    16. present: It says "campus", a location.
    17. present: It refers to "campus".
    18. present: It references "campus" as the location.
    19. present: "campus" is specified as the location.
    20. present: It references "campus", a location.
    21. present: It cites "campus", a location.
    22. present: It cites "campus", a location.
    23. present: It says "campus", a location.
    24. present: It references "campus" as the threatened location.
    25. present: It cites "campus", a location reference.
  • Guidancepresent25/25

    Final assessment

    All 25 reads agree guidance is present; the alert instructs recipients to "Calmly leave campus".

    The protective action to take. A clear, specific instruction, such as shelter in place, evacuate, avoid the area, or run-hide-fight, drives faster and more correct protective behavior than describing the threat alone.

    See all 25 individual reads
    1. present: "Calmly leave campus" instructs a protective action.
    2. present: It instructs to "Calmly leave campus", a protective action.
    3. present: It instructs "Calmly leave campus", a protective action.
    4. present: It instructs recipients to "Calmly leave campus".
    5. present: It instructs "Calmly leave campus", a protective action.
    6. present: It instructs "Calmly leave campus", a protective action.
    7. present: It instructs people to "Calmly leave campus".
    8. present: "Calmly leave campus" is a protective instruction.
    9. present: It instructs "Calmly leave campus", a protective action.
    10. present: It instructs "Calmly leave campus", a protective action.
    11. present: It instructs recipients to "Calmly leave campus", a protective action.
    12. present: It instructs "Calmly leave campus", a protective action.
    13. present: It instructs recipients to "Calmly leave campus".
    14. present: It instructs "Calmly leave campus".
    15. present: "Calmly leave campus" is a protective instruction.
    16. present: It instructs "Calmly leave campus", a protective action.
    17. present: It instructs "Calmly leave campus".
    18. present: It instructs recipients to "Calmly leave campus".
    19. present: "Calmly leave campus" is a protective instruction.
    20. present: It instructs "Calmly leave campus", a protective action.
    21. present: It instructs "Calmly leave campus", a protective action.
    22. present: It instructs recipients to "Calmly leave campus", a protective action.
    23. present: It instructs "Calmly leave campus", a protective action.
    24. present: It instructs "Calmly leave campus", a protective action.
    25. present: "Calmly leave campus" is a protective action instruction.
  • Timepresent25/25

    Final assessment

    All 25 reads agree timing is present; the message gives clock times of 2:45pm and until at least 4:30pm.

    When the message applies. A timestamp, the word now or immediately, or a phrase like until further notice tells the reader whether the danger is current and how quickly to act.

    See all 25 individual reads
    1. present: "at 2:45pm" and "until at least 4:30pm" convey clock times.
    2. present: It gives clock times: "2:45pm" and "until at least 4:30pm".
    3. present: It gives clock times "at 2:45pm" and "until at least 4:30pm".
    4. present: It gives clock times: "at 2:45pm" and "closed until at least 4:30pm".
    5. present: It gives times "at 2:45pm" and "closed until at least 4:30pm".
    6. present: It says "at 2:45pm" and "until at least 4:30pm", clock times.
    7. present: It gives clock times, "at 2:45pm" and "until at least 4:30pm".
    8. present: "at 2:45pm" and "until at least 4:30pm" are clock times.
    9. present: It gives clock times: "at 2:45pm" and "until at least 4:30pm".
    10. present: It gives "at 2:45pm" and "until at least 4:30pm", clock-time cues.
    11. present: It gives times: "at 2:45pm" and "until at least 4:30pm".
    12. present: It gives "2:45pm" and "until at least 4:30pm", specific clock times.
    13. present: It gives clock times: "at 2:45pm" and closed "until at least 4:30pm".
    14. present: It states the report time "at 2:45pm" and closure "until at least 4:30pm".
    15. present: "at 2:45pm" and "until at least 4:30pm" give clock times.
    16. present: It says "at 2:45pm" and "until at least 4:30pm", clock-time cues.
    17. present: It gives times: "at 2:45pm" and "until at least 4:30pm".
    18. present: It gives clock times "2:45pm" and "until at least 4:30pm".
    19. present: "at 2:45pm" and "until at least 4:30pm" give specific times.
    20. present: It gives "2:45pm" and "until at least 4:30pm", clock-time cues.
    21. present: "at 2:45pm" and "until at least 4:30pm" give specific clock times.
    22. present: It cites "at 2:45pm" and "until at least 4:30pm", explicit clock times.
    23. present: It gives "2:45pm" and "until at least 4:30pm", clock times.
    24. present: It gives times: "at 2:45pm" and "until at least 4:30pm".
    25. present: "at 2:45pm" and "until at least 4:30pm" give specific times.
  • Impactabsent0/25

    Final assessment

    Absent by unanimous agreement; a report of a threat with a leave-campus order names no specific hazard and states no potential harm or consequence.

    What the hazard could do to the people in its path. Beyond naming the threat, a complete warning conveys its potential consequences or severity, such as that a tornado can level buildings or that a leak could be explosive, so recipients grasp how much danger they are in. Research on warning message content finds that a concrete impact statement helps people personalize their risk and act sooner.

    See all 25 individual reads
    1. absent: A report of a threat to campus prompting evacuation states no consequence or specific harm.
    2. absent: Reports a threat to campus and says calmly leave but states no specific harm or potential consequence.
    3. absent: Reports a threat to campus and tells people to leave but states no harm or how dangerous it is.
    4. absent: Reports a threat to campus with instructions to leave but states no specific hazard or harm.
    5. absent: It reports a threat to campus and to calmly leave but states no consequence or danger.
    6. absent: It reports a threat to campus and a closure but does not state the nature or severity of the danger.
    7. absent: Reports a threat and tells people to leave campus but states no potential harm or severity.
    8. absent: A threat to campus with instruction to leave but no stated danger or potential harm.
    9. absent: Reports a threat to campus and tells people to leave but states no consequence or severity.
    10. absent: A reported threat to campus with calm-departure and closure instructions states no specific harm or consequence.
    11. absent: It reports a threat to campus and orders people to leave but states no specific harm or severity.
    12. absent: Reports a threat and campus closure but does not state any harm or how dangerous the threat is.
    13. absent: A report of threat to campus with calm-departure instructions states no consequence or severity.
    14. absent: Reports a threat to campus and a closure but states no potential harm or severity.
    15. absent: It cites a threat to campus and a closure but states no consequence or severity.
    16. absent: References a threat to campus with a calmly-leave directive but states no specific danger or harm.
    17. absent: Reports a threat to campus and to calmly leave but states no danger or potential consequence.
    18. absent: It cites a threat and tells people to leave campus but states no specific harm or severity.
    19. absent: A report of a threat with calmly-leave-campus guidance states no specific harm or hazard severity.
    20. absent: Names a threat to campus and to leave but states no explicit danger or consequence.
    21. absent: It reports a threat and closes campus but states no specific danger or potential harm.
    22. absent: It reports a threat and tells people to leave campus but states no harm or severity of the threat.
    23. absent: Reports a threat to campus and orders calm evacuation but states no potential harm or severity.
    24. absent: Reports a threat and tells people to leave campus but states no specific harm or severity.
    25. absent: Reports a threat to campus and campus closure but states no specific harm or consequence.

Systematic AI judgments with visible reasoning, not human-validated codings.

About this analysis
Context

Background

Mt. San Antonio College, known as Mt. SAC, is one of the largest community colleges in California, located in Walnut, eastern Los Angeles County. On the morning of Thursday, March 24, 2016, at 10:24 a.m. PDT, Mt. SAC and adjacent Walnut High School received a bomb threat that named a 2:45 p.m. PDT detonation time, an unusually specific time, which gave the Los Angeles County Sheriff's Department and Mt. SAC administrators a four-hour window to act. Mt. SAC was evacuated; Walnut High School, where students were minors who could not be released without parent pickup, was placed on lockdown. LASD deputies with bomb-detection K-9 units swept both campuses. At approximately 1:22 p.m. PDT, LASD tweeted that the threat had concluded and the lockdown at Walnut High School had been lifted. Mt. SAC's separate all-clear came at approximately 3:11 p.m. PDT (about 26 minutes after the named detonation time) and the college announced that classes would resume at 4:30 p.m. PDT. On April 6, 2016, 18-year-old Adrian Mendoza of West Covina, enrolled at both Walnut High School and Mt. SAC, was arrested on suspicion of making a false report of a bomb or explosive device. The case is significant for the campus alert archive because it documents joint community-college and K-12 emergency-management coordination, a pattern recurring in California, where many community colleges sit immediately adjacent to high schools, and because the named-time bomb threat created an unusually structured decision window for administrators and law enforcement.
Analysis

Key Findings

The bomb threat named a specific detonation time (2:45 p.m. PDT) that gave administrators an unusually structured four-hour decision window
Mt. SAC was evacuated while adjacent Walnut High School was placed on lockdown, different protocols reflecting K-12 vs community-college student-release rules
LASD bomb-detection K-9 units swept both campuses, the standard Los Angeles County protocol for community-college bomb threats
Walnut High School's lockdown was lifted at 1:22 p.m. PDT after LASD tweeted that the threat had concluded; Mt. SAC's separate all-clear was issued at approximately 3:11 p.m. PDT, with classes resuming at 4:30 p.m. PDT
On April 6, 2016, 18-year-old Adrian Mendoza of West Covina, enrolled at both Walnut High School and Mt. SAC, was arrested on suspicion of making a false report of a bomb or explosive device
Outcome
No device was found. The Walnut High School lockdown was lifted at 1:22 p.m. PDT after LASD tweeted the conclusion of the threat. Mt. SAC tweeted at approximately 3:11 p.m. PDT that the campus was clear, with classes scheduled to resume at 4:30 p.m. PDT. The threat was treated as a hoax; LASD bomb squad with K-9 units cleared both campuses well before the named 2:45 p.m. PDT detonation time. On April 6, 2016, 18-year-old Adrian Mendoza of West Covina, enrolled at both Walnut High School and Mt. SAC, was arrested on suspicion of making a false report of a bomb or explosive device.
Provenance

Sources

  1. News
    Bomb threat closes Mt. SAC College, prompts lockdown of Walnut High School (ABC7 Los Angeles)
    abc7.com
    archived copy
  2. News
    Mount San Antonio College Evacuated Amid Possible Bomb Threat; Walnut High School on Lockdown (KTLA)
    ktla.com
    archived copy
  3. News
    All-Clear Given After Bomb Threat at Mt. San Antonio College (NBC Los Angeles)
    nbclosangeles.com
    archived copy
  4. News
    Evening Classes To Resume At Mount San Antonio College In Walnut Following Threat (CBS Los Angeles)
    cbsnews.com
    archived copy
  5. News
    Mt. San Antonio College, Walnut High declared safe after bomb threat (89.3 KPCC)
    archive.kpcc.org
    archived copy
  6. Student Paper
    Bomb threat closes Mt. SAC and Walnut High School (Campus Times)
    lvcampustimes.org
    archived copy
  7. News
    18-Year-Old Student Arrested in False Bomb Threat at Mt. San Antonio College (NBC Los Angeles)
    nbclosangeles.com
    archived copy
Cite this case

Campus Alert Archive. "Mt. San Antonio College: Bomb threat with a stated detonation time evacuated campus; determined to be a hoax." Incident of March 24, 2016. Added May 2026. https://campusalertarchive.com/case/mt-san-antonio-college-bomb-threat-2016-03-24/

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Alert text quoted on this page remains the work of the issuing institution; the archive is a secondary source.

Tags
bomb-threatcommunity-collegecaliforniawalnutlos-angeles-countyk-12-coordinationnamed-detonation-timeevacuationlasd-bomb-squadk9-sweepHoax
Added May 2026Updated May 2026Via ingestion