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
Official alert policy
Read when and how Mt. SAC says it will use Mt. SAC Emergency Notification System: summarized, quoted, and analyzed.
Documented Timeline

Alert Sequence

3 messages in sequence · 1 verified verbatim

Confirmed wording is transcribed character-for-character from a primary source. Use Verify this quote under each message to open that source in a new tab and compare the text yourself.

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 verbatim139 chars
EMERGENCY ALERT: Report of threat to campus at 2:45pm. Calmly leave campus. Classes/services are closed until at least 4:30pm. NOT A DRILL.
Verify this quote
ABC7 Los Angeles, quoting the Mt. SAC emergency alert text message sent to studentsx.comfind archived copies
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
DEEP AUDIT correct 2026-08-02: abc7.com live; only paraphrases ('calmly leave campus'; closed until 4:30). Full @MtSAC tweet adds trailing 'NOT A DRILL' archive omits. Correct to full social artifact; re-source X.
UPDATEEmail
Wording not yet recovered

A message was sent at this point in the sequence; its exact wording has not yet been recovered from the official record, so no text is shown. This site never paraphrases or reconstructs alert wording. Markers like this one keep the emergency's true shape and become word-for-word messages as recovery reaches the source.

ALL CLEARSMS
Wording not yet recovered

A message was sent at this point in the sequence; its exact wording has not yet been recovered from the official record, so no text is shown. This site never paraphrases or reconstructs alert wording. Markers like this one keep the emergency's true shape and become word-for-word messages as recovery reaches the source.

Reconstructed from CBS Los Angeles reporting on Mt. SAC's 3:11 p.m. PDT tweet declaring campus safe and resumption of classes at 4:30 p.m. PDT
Message elements

How the first alert is built

To check this alert, Claude Opus 5 (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. NOT A DRILL.

  • Sourceabsent0/25

    Final assessment

    Unanimous: absent. The message opens only with the generic label EMERGENCY ALERT and never names the college, an agency, or a branded alert system.

    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. absent: Only the generic label "EMERGENCY ALERT" appears, naming no institution or agency.
    2. absent: Only the generic words "EMERGENCY ALERT" appear, with no institution or agency named.
    3. absent: Only the generic label "EMERGENCY ALERT" appears, with no institution or agency named.
    4. absent: Only the generic words "EMERGENCY ALERT" appear, with no institution or agency named.
    5. absent: It opens only with "EMERGENCY ALERT", naming no institution or agency.
    6. absent: "EMERGENCY ALERT" is a generic label, not a branded system or named agency.
    7. absent: Only "EMERGENCY ALERT" appears, with no institution, agency, or branded sender named.
    8. absent: Only the generic words "EMERGENCY ALERT" appear, with no institution or agency named.
    9. absent: Only the generic label "EMERGENCY ALERT" appears, with no institution or agency named.
    10. absent: Only the words "EMERGENCY ALERT" appear, with no institution, agency, or brand name.
    11. absent: Only the generic label "EMERGENCY ALERT" appears, with no institution or agency named.
    12. absent: "EMERGENCY ALERT" is a generic label, not a branded sender or named agency.
    13. absent: Only the generic label "EMERGENCY ALERT" appears, with no institution or agency named.
    14. absent: It opens only with "EMERGENCY ALERT" and names no institution, agency, or branded system.
    15. absent: Only the generic words "EMERGENCY ALERT" appear, with no institution or agency named.
    16. absent: "EMERGENCY ALERT" is generic wording, naming no institution or agency.
    17. absent: Only the generic words "EMERGENCY ALERT" appear, with no branded name or agency.
    18. absent: Only "EMERGENCY ALERT" appears, with no institution, agency, or branded sender name.
    19. absent: "EMERGENCY ALERT" is a generic label, and no institution or agency names itself.
    20. absent: It says only "EMERGENCY ALERT" with no institution, agency, or branded sender name.
    21. absent: "EMERGENCY ALERT" is a generic label and no institution or agency names itself.
    22. absent: The generic header "EMERGENCY ALERT:" names no institution, agency, or branded system.
    23. absent: Only the words "EMERGENCY ALERT" appear, with no institution, agency, or branded system name.
    24. absent: Only the generic label EMERGENCY ALERT appears, with no institution or agency named.
    25. absent: Only the generic header "EMERGENCY ALERT" appears, with no institution or agency named.
  • Hazardabsent1/25

    Final assessment

    Near unanimous: absent. It reports a threat to campus without saying what kind of threat, and a single dissenting read treated that generic wording as specific enough.

    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: It says "Report of threat to campus" without naming what the threat is.
    2. absent: It says "threat to campus" without naming what kind of threat it is.
    3. absent: It says "Report of threat to campus" without naming what the threat is.
    4. absent: It cites a "threat to campus" without naming what the threat is.
    5. absent: It says "Report of threat to campus" without naming the specific hazard.
    6. absent: "Report of threat to campus" is generic and names no specific hazard.
    7. absent: It says "threat to campus" generically without naming what the threat is.
    8. absent: "Report of threat to campus" is generic and does not name a specific hazard.
    9. absent: "threat to campus" is unspecific and does not name the hazard.
    10. absent: It says "threat to campus" without naming what the threat actually is.
    11. absent: It says only "threat to campus" without naming what kind of threat.
    12. absent: It says only "threat to campus", which does not name a specific hazard.
    13. absent: It says "threat to campus" without naming what the threat is.
    14. absent: It says "threat to campus" without naming what the threat is.
    15. absent: "Report of threat to campus" is generic and names no specific hazard.
    16. absent: A "threat to campus" is stated without saying what kind of threat.
    17. absent: A "threat to campus" is generic and does not name the specific hazard.
    18. absent: "threat to campus" is generic and names no specific hazard.
    19. absent: It says only "threat to campus" without specifying bomb, shooter, or any concrete hazard.
    20. absent: It reports a "threat to campus" without naming what the threat is.
    21. absent: It says only "threat to campus", which does not specify the hazard.
    22. absent: It says only "threat to campus", which does not name a specific hazard.
    23. absent: A "threat to campus" is generic and does not identify the actual hazard.
    24. present: It reports a threat to campus, a specific hazard.
    25. absent: "threat to campus" is generic and does not specify what the threat is.
  • Locationpresent25/25

    Final assessment

    Unanimous: present. The message names campus as the affected place, which the reads accepted as the location at risk.

    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 place reference.
    2. present: It refers to "campus" as the affected place.
    3. present: It refers to "campus" as the threatened place.
    4. present: It refers to "campus" as the affected place.
    5. present: It says the threat is to "campus".
    6. present: It refers to "campus" as the affected place.
    7. present: It refers to "campus" as the affected place.
    8. present: It refers to "campus" as the affected place.
    9. present: It refers to "campus" as the affected place.
    10. present: It refers to "campus", a location.
    11. present: It refers to "campus", a location reference.
    12. present: It refers to "campus", a place.
    13. present: It refers to "campus" as the affected place.
    14. present: It refers to "campus" as the affected place.
    15. present: It refers to "campus" as the affected place.
    16. present: It refers to campus as the affected place.
    17. present: Refers to "campus" as the affected place.
    18. present: It says the threat is to "campus" and instructs leaving campus.
    19. present: It refers to "campus" as the place affected.
    20. present: It refers to "campus", a location.
    21. present: It refers to "campus", a location.
    22. present: It refers to "campus", a location reference.
    23. present: It refers to "campus" as the affected area.
    24. present: It refers to campus as the place to leave.
    25. present: It refers to "campus" as the affected place.
  • Guidancepresent25/25

    Final assessment

    Unanimous: present. Recipients are told to calmly leave campus, a direct protective instruction, reinforced by the closure notice.

    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: It instructs recipients to "Calmly leave campus".
    2. present: It instructs recipients to "Calmly leave campus".
    3. present: It instructs people to "Calmly leave campus".
    4. present: It instructs people to "Calmly leave campus".
    5. present: It instructs people to "Calmly leave campus".
    6. present: It instructs recipients to "Calmly leave campus".
    7. present: It instructs people to "Calmly leave campus".
    8. present: It instructs recipients to "Calmly leave campus".
    9. present: It tells recipients to "Calmly leave campus".
    10. present: It instructs recipients to "Calmly leave campus".
    11. present: It instructs recipients to "Calmly leave campus".
    12. present: It instructs people to "Calmly leave campus".
    13. present: It tells people to "Calmly leave campus".
    14. present: It instructs recipients to "Calmly leave campus".
    15. present: It tells people to "Calmly leave campus".
    16. present: It instructs people to "Calmly leave campus".
    17. present: Instructs people to "Calmly leave campus".
    18. present: It tells recipients to "Calmly leave campus".
    19. present: It instructs recipients to "Calmly leave campus".
    20. present: It instructs readers to "Calmly leave campus".
    21. present: It instructs people to "Calmly leave campus".
    22. present: It directs people to "Calmly leave campus".
    23. present: It instructs recipients to "Calmly leave campus".
    24. present: It instructs recipients to calmly leave campus.
    25. present: It instructs recipients to "Calmly leave campus".
  • Timepresent25/25

    Final assessment

    Unanimous: present. Two clock times are given, the 2:45pm report and closure 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: It gives the times "2:45pm" and "until at least 4:30pm".
    2. present: It gives clock times, "2:45pm" and "until at least 4:30pm".
    3. present: It gives clock times: "2:45pm" and "closed until at least 4:30pm".
    4. present: It gives "2:45pm" and "until at least 4:30pm".
    5. present: It gives "2:45pm" and "until at least 4:30pm".
    6. present: It gives "2:45pm" and "closed until at least 4:30pm".
    7. present: It gives clock times "2:45pm" and "until at least 4:30pm".
    8. present: It gives "2:45pm" and "until at least 4:30pm".
    9. present: It gives clock times "2:45pm" and "until at least 4:30pm".
    10. present: It gives "2:45pm" and "until at least 4:30pm".
    11. present: It gives clock times "2:45pm" and "until at least 4:30pm".
    12. present: It gives clock times, "2:45pm" and "until at least 4:30pm".
    13. present: It gives clock times, "at 2:45pm" and "until at least 4:30pm".
    14. present: It gives clock times "2:45pm" and "until at least 4:30pm".
    15. present: It gives clock times "2:45pm" and "until at least 4:30pm".
    16. present: It gives clock times: "2:45pm" and "until at least 4:30pm".
    17. present: Gives clock times "2:45pm" and "until at least 4:30pm".
    18. present: It gives clock times "2:45pm" and "until at least 4:30pm".
    19. present: It gives clock times: the report "at 2:45pm" and closure "until at least 4:30pm".
    20. present: It gives the clock times "2:45pm" and "4:30pm".
    21. present: It gives the clock times "2:45pm" and "until at least 4:30pm".
    22. present: It gives clock times, "at 2:45pm" and "until at least 4:30pm".
    23. present: It gives clock times: "2:45pm" and "until at least 4:30pm".
    24. present: It gives clock times, 2:45pm and until at least 4:30pm.
    25. present: It gives clock times: "2:45pm" and closure "until at least 4:30pm".
  • Impactabsent1/25

    Final assessment

    Near unanimous: absent. NOT A DRILL stresses that the event is real but describes no harm or severity, and only one read counted that emphasis as impact.

    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: "NOT A DRILL" stresses reality but states no consequence or severity of harm.
    2. absent: Beyond "NOT A DRILL" it states no consequence or severity of harm.
    3. absent: "NOT A DRILL" stresses reality but no harm or severity is described.
    4. absent: "NOT A DRILL" stresses reality but names no consequence or harm.
    5. absent: "NOT A DRILL" stresses reality but states no consequence or severity.
    6. absent: "NOT A DRILL" stresses reality but states no consequence or harm.
    7. absent: No potential harm or severity is described; "NOT A DRILL" asserts reality, not consequence.
    8. absent: "NOT A DRILL" asserts authenticity but conveys no consequence or severity of harm.
    9. absent: "NOT A DRILL" stresses reality but states no consequence or harm.
    10. absent: "NOT A DRILL" stresses reality but states no consequence or harm.
    11. absent: "NOT A DRILL" stresses reality but states no consequence or severity of harm.
    12. absent: "NOT A DRILL" stresses reality but states no consequence or severity.
    13. absent: "NOT A DRILL" asserts reality but states no consequence or harm.
    14. absent: "NOT A DRILL" stresses reality but states no consequence or severity of harm.
    15. absent: No description of potential harm; "NOT A DRILL" asserts reality, not consequence.
    16. absent: "NOT A DRILL" stresses reality, not consequences or severity of harm.
    17. present: "NOT A DRILL" plus closure emphasizes the seriousness of the threat.
    18. absent: "NOT A DRILL" stresses reality but states no potential harm or severity.
    19. absent: "NOT A DRILL" stresses reality but states no consequence or level of harm.
    20. absent: "NOT A DRILL" stresses reality but states no consequence or harm.
    21. absent: "NOT A DRILL" stresses reality but states no consequence or degree of harm.
    22. absent: No consequence is described, though "NOT A DRILL" stresses reality rather than harm.
    23. absent: No harm or severity is described; "NOT A DRILL" states authenticity, not consequence.
    24. absent: No harm or severity is described; NOT A DRILL asserts reality, not consequence.
    25. absent: "NOT A DRILL" stresses reality but states no consequence or severity of harm.

Coded by Claude Opus 5

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

Every claim on this page is meant to be checkable. Open the links below (and the Verify this quote control under each confirmed alert) to read the original university, news, or archive page yourself. Hostnames are shown so you can see where you are going; archived copies survive when live pages move or disappear. See also our methodology.

  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
  8. News
    ABC7 Los Angeles, quoting the Mt. SAC emergency alert text message sent to students
    abc7.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; last updated August 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 August 2026Via ingestion