MINE DETAILS
Twin Mountain Rock Venture
MSHA MINE ID0403623
LOCATION
Mine location
1 of 1 mine with usable MSHA coordinates. Select a marker to open a mine.
Mine coordinates
- Twin Mountain Rock Venture35.98306, -117.91194Open map ↗
Quarterly trends
2025 Q1 – 2026 Q4
Database snapshot · 2026-10-18. MSHA quarterly production and employment reports.
Coal production
0reported short tons
Hours worked
12,754reported employee hours
Tons per hour
0.00production ÷ hours worked
Missing values appear as —. Totals use available reports. Tons per hour requires production and hours for the same quarters and a nonzero hours total. * Striped bars mark partial mine coverage or an incomplete quarter. See the table for coverage.
Quarterly data and reporting coverage
| Quarter | Coal (short tons) | Hours worked | Tons / hour | Avg. employees | Coverage |
|---|---|---|---|---|---|
| 2025 Q1 | 0 | 1,796 | 0.00 | 4 | 1/1 mines reporting |
| 2025 Q2 | 0 | 2,409 | 0.00 | 4 | 1/1 mines reporting |
| 2025 Q3 | 0 | 1,999 | 0.00 | 4 | 1/1 mines reporting |
| 2025 Q4 | 0 | 2,268 | 0.00 | 4 | 1/1 mines reporting |
| 2026 Q1 | 0 | 1,852 | 0.00 | 4 | 1/1 mines reporting |
| 2026 Q2 | 0 | 2,430 | 0.00 | 4 | 1/1 mines reporting |
| 2026 Q3 | — | — | — | — | No report |
| 2026 Q4 | — | — | — | — | No report |
Safety and enforcement
2025-01-01 – 2026-10-18
Violations
20 significant & substantial (S&S)
Accident records
00 records classified as fatality
Proposed penalties · USD
316.002 of 2 violations with amounts
On-site inspection hours
23.005 inspections · 5 with hours
Counts are published records, including contractor records. * The quarter was incomplete at the snapshot date; recent counts may rise as reports arrive. — means no reported amount or hours. Portfolio totals use current membership.
Quarterly safety data
| Quarter | Violations | S&S | Proposed USD | Accident records | Fatality records | Inspections | On-site hours |
|---|---|---|---|---|---|---|---|
| 2025-Q1 | 1 | 0 | 151.00 | 0 | 0 | 1 | 5.0 |
| 2025-Q2 | 0 | 0 | — | 0 | 0 | 0 | — |
| 2025-Q3 | 0 | 0 | — | 0 | 0 | 1 | 5.0 |
| 2025-Q4 | 0 | 0 | — | 0 | 0 | 0 | — |
| 2026-Q1 | 1 | 0 | 165.00 | 0 | 0 | 1 | 4.0 |
| 2026-Q2 | 0 | 0 | — | 0 | 0 | 0 | — |
| 2026-Q3 | 0 | 0 | — | 0 | 0 | 1 | 5.0 |
| 2026-Q4 * | 0 | 0 | — | 0 | 0 | 1 | 4.0 |
Most cited CFR sections
All violations issued in the selected period. Counts combine subsections.
| Section | Violations | S&S |
|---|---|---|
| 30 CFR 46.3Training plans. | 1 | 0 |
| 30 CFR 56.12032Inspection and cover plates. | 1 | 0 |
Safety activity
No matching records in this period.
Safety sources and definitions
MSHA Violations (issue date), Accidents (accident date), and Inspections (begin date). Snapshot 2026-10-18.
Counts describe published rows, including contractor records; accident records are not distinct incidents or numbers of people injured.
Zero means no matching records in the imported sources, not proof of no events. Historical coverage differs by source; absence before a source begins reporting is not a zero incident rate. Invalid or absent dates and records after the snapshot are excluded.
S&S means SIG_SUB=Y. Fatality records use DEGREE_INJURY_CD=01. Proposed penalties are not final assessed or paid amounts; missing dollar values are omitted.
Inspection hours are SUM_TOTAL_ON_SITE_HOURS attributed to the inspection start date, without supervisor/trainee hours. Missing hours are omitted; a started inspection may still be open.
Portfolio totals use current mine membership, including events before the current owner or operator's tenure.
CFR headings link to the current Title 30 index; they are not historical legal determinations.
OWNERSHIP
Operator and controller history
Current ownership comes from MSHA Mines. Historical start and end dates come from MSHA Controller and Operator History.
—
Eddie AntoninicontrolsTwin Mountain Rock VentureoperatesTwin Mountain Rock Venture
msha-controller-operator-history · controller/operator co-tenure derived on mine 0403623—
Cemex S AcontrolsCemex Construction Materials LPoperatesTwin Mountain Rock Venture
msha-controller-operator-history · controller/operator co-tenure derived on mine 0403623—
Cemex S AcontrolsRinker Materials Western IncoperatesTwin Mountain Rock Venture
msha-controller-operator-history · controller/operator co-tenure derived on mine 0403623—
Rinker Group LtdcontrolsRinker Materials Western IncoperatesTwin Mountain Rock Venture
msha-controller-operator-history · controller/operator co-tenure derived on mine 0403623—
CSR LtdcontrolsRinker Materials Western IncoperatesTwin Mountain Rock Venture
msha-controller-operator-history · controller/operator co-tenure derived on mine 0403623—
Angelus Block Co et alcontrolsTwin Mountain Rock VentureoperatesTwin Mountain Rock Venture
msha-controller-operator-history · controller/operator co-tenure derived on mine 0403623—
Kiewit Peter Sons' Inc et alcontrolsTwin Mountain Rock VentureoperatesTwin Mountain Rock Venture
msha-controller-operator-history · controller/operator co-tenure derived on mine 0403623—
Peter Kiewit Sons' InccontrolsTwin Mountain Rock CompanyoperatesTwin Mountain Rock Venture
msha-controller-operator-history · controller/operator co-tenure derived on mine 0403623Other historical summaries · source-specific periods
RECORD SUMMARY
Production, safety and enforcement
These summaries use the periods stated on each card, independently of the reporting period above.
01 / SAFETYwatch
Accidents and injuries
6 historical accident/injury rows; 0 coded fatalities and 270 lost days across the published record.
ACCIDENT + INJURY RECORD1 since 2021
accidentsmine-production-quarterly02 / COMPLIANCEwatch
Violations and penalties
160 violation rows across the full record; 40 carry an S&S flag and $51,392 appears in current assessed amounts.
ENFORCEMENT ACTIVITY26 since 2021
inspectionsviolationsassessed-violationsorders-107a03 / HEALTHcontext
Occupational health samples
12 personal. 0 personal-sample rows have a published C/E ratio above 1; 0 noise rows have an action-level or PEL dose above 100%. These are separate measures, not a silica exceedance count. Silica results and sample status are shown separately.
OCCUPATIONAL EXPOSURE12 samples
personal-health-samples04 / PRODUCTIONcontext
Quarterly production and employment
2K employee hours and 4 summed average employees across reported subunits in the latest published quarter.
2026-Q20 tons
mine-production-quarterlymine-production-yearly05 / LEGALwatch
Contests, conferences and decisions
3 contested-violation rows, 3 civil-penalty docket/decision rows, and 10 conference records linked by issuance number.
POST-ISSUANCE LIFECYCLE16 linked rows
conferencescontested-violationscivil-penalty-dockets-decisions06 / CONTRACTORScontext
Contractors
Contractors are linked through this mine’s violation or accident records. Their production and hours cover all their operations, so they are not included in this mine’s totals.
ENTITY-LEVEL CONTEXT0 linked entities
contractor-production-quarterlycontractor-production-yearlyaccidentsviolations07 / INSPECTIONScontext
Inspections
79 inspection events and 1K published inspection hours across the historical record.
OVERSIGHT COVERAGE15 since 2021
inspectionsviolationsHEALTH SAMPLING
Silica and quartz
Coal quartz, metal/nonmetal personal samples and area samples. Snapshot Oct 18, 2026. 3 silica records across the mine’s published history.
Personal silica samples · concentration / limit
Quarterly mean · published C/E ratio
— No eligible measurements. * Quarter in progress. Means describe the available samples, not average exposure across the mine.
Quartz % is the sample’s quartz content; µg/m³ is its reported concentration. Personal C/E is the ratio to the limit published with that sample. Personal and area concentration units and void status are not specified in those source files.
| Date / sample | Dataset / analyte | Occupation / area | Measurement | Sample status | Published action |
|---|---|---|---|---|---|
| 000000202603724300 | Metal/nonmetal personalQuartz, respirable, >1% Qtz | Front-end Loader Operator | 0× published limitConcentration: 0000.13 · limit: 0000.00Source unit unspecified | Not reported | NO ACTIONInspection F020C31 |
Sources and interpretation
- Coal means use numeric concentrations from samples marked not voided, excluding control/invalid sample types and dates after the snapshot. Missing values remain null; reported zeroes remain zero.
- Quarterly means describe available samples, not mine-wide or worker-average exposure. Quarters with no eligible measurements remain empty; the current quarter is partial.
- Personal C/E is MSHA's published concentration-to-limit ratio. A value above 1 is not by itself a citation or a determination under the 2024 silica rule. Personal and area files do not publish a void-status field.
- Area records include bulk-dust analyses and are kept separate from personal exposure results. Their concentration units are not specified in the source dictionary.
- Missing samples do not establish safe conditions. Coal quartz percentage and concentration are separate measures. No compliance threshold is inferred for coal samples.
Coal quartz field definitions ↗Metal/nonmetal personal field definitions ↗Metal/nonmetal area field definitions ↗
EIA + TITLE 30
EIA production and cited regulations
EIA annual figures are reported separately from MSHA. Regulation links use the current eCFR snapshot.
Not present in the 2024 EIA coal workbook.
This can mean the operation is non-coal, inactive for the annual period, or outside the EIA-7A reporting population.
30 CFR 46.3Training plans.2 recent rows ↗30 CFR 56.12032Inspection and cover plates.2 recent rows ↗30 CFR 47.31Requirement for a HazCom program.1 recent row ↗30 CFR 56.12018Identification of power switches.1 recent row ↗30 CFR 56.12002Controls and switches.1 recent row ↗30 CFR 56.12004Electrical conductors.2 recent rows ↗30 CFR 56.14207Parking procedures for unattended equipment.1 recent row ↗30 CFR 56.14107Moving machine parts.1 recent row ↗
RECENT PUBLIC RECORDS
Recent violations and samples
Latest records retained for inspection; aggregates above use the full source history.
516513646.3(b)(4)Citation
950799956.12032Citation
950057146.3(b)Citation
950057047.31(a)Citation
950056956.12018Citation
950056856.12002Citation
950056756.12032S&S
950056656.12004Citation
Coal dust, noise and other contaminants. Silica records above ↑
Unlisted Particulate, respirable, <1% QtzFront-end Loader Operator
C/E: 00.00Concentration: 0000.55 · limit: 0000.00Source unit unspecified
Respirable dust, <.1mgUtility Man
C/E: 00.00Concentration: 0000.00 · limit: 0000.00Source unit unspecified
Unlisted Particulate, respirable, <1% QtzCleanup Man
C/E: 00.00Concentration: 0000.33 · limit: 0000.00Source unit unspecified
Respirable dust, <.1mgScale Man
C/E: 00.00Concentration: 0000.00 · limit: 0000.00Source unit unspecified
Unlisted Particulate, respirable, <1% QtzCrusher Oper/Worker
C/E: 00.00Concentration: 0000.45 · limit: 0000.00Source unit unspecified
Respirable dust, <.1mgFront-end Loader Operator
C/E: 00.00Concentration: 0000.00 · limit: 0000.00Source unit unspecified
Respirable dust, <.1mgFront-end Loader Operator
C/E: 00.00Concentration: 0000.00 · limit: 0000.00Source unit unspecified
Unlisted Particulate, respirable, <1% QtzCrusher Oper/Worker
C/E: 00.00Concentration: 0000.15 · limit: 0000.00Source unit unspecified
SOURCE COVERAGE
Reporting dates and coverage
13 datasets contain linked records. Missing datasets are listed below.
DATASETROWSWINDOWSTATUS
Accident, Injuries, and Illnessessafety · contractors6May 22, 2006—Jun 7, 2021mine-keyed
Addresses of Recordidentity · logistics1Nov 21, 1979—Nov 21, 1979mine-keyed
Assessed Violationscompliance · legal159Aug 17, 2000—Feb 11, 2026mine-keyed
Civil Penalty Dockets and Decisionscompliance · legal3Nov 20, 2008—Apr 28, 2016mine-keyed
Coal Dust Sampleshealth · safety—No published rowsabsent / not applicable
Conferencescompliance · legal10Oct 13, 2000—Jul 28, 2021mine-keyed
Contested Violationscompliance · legal3Dec 4, 2007—May 8, 2014mine-keyed
Contractor Employment and Production — Quarterlycontractors · production · safety—No published rowsabsent / not applicable
Contractor Employment and Production — Yearlycontractors · production · safety—No published rowsabsent / not applicable
Controller and Operator Historyidentity · compliance8Dec 1, 1979—May 29, 2015mine-keyed
Mine Employment and Production — Quarterlyproduction · safety · compliance205Not published—Not publishedmine-keyed
Mine Employment and Production — Yearlyproduction · safety · compliance48Not published—Not publishedmine-keyed
Inspectionssafety · compliance79Aug 17, 2000—Oct 7, 2026mine-keyed
Minesidentity · production · logistics1Not published—Not publishedmine-keyed
Metal and Nonmetal Area Sampleshealth · safety—No published rowsabsent / not applicable
Metal and Nonmetal Personal Health Sampleshealth · safety12May 1, 2002—Sep 2, 2026mine-keyed
Noise Sampleshealth · safety · equipment—No published rowsabsent / not applicable
Quartz Samples — Coalhealth · safety—No published rowsabsent / not applicable
Violationscompliance · safety · legal160Aug 17, 2000—Feb 11, 2026mine-keyed
107(a) Orders Issuedsafety · compliance—No published rowsabsent / not applicable
NOTES
Limitations
- Contractor production is entity-level and is never represented as mine-attributable.
- Missing rows can mean no event, publication delay, identity mismatch, or inapplicability.