diff --git a/spark/src/test/resources/sql-tests/expressions/datetime/trunc_timestamp_dst.sql b/spark/src/test/resources/sql-tests/expressions/datetime/trunc_timestamp_dst.sql
new file mode 100644
index 0000000000..ebb75d56e6
--- /dev/null
+++ b/spark/src/test/resources/sql-tests/expressions/datetime/trunc_timestamp_dst.sql
@@ -0,0 +1,62 @@
+-- Licensed to the Apache Software Foundation (ASF) under one
+-- or more contributor license agreements.  See the NOTICE file
+-- distributed with this work for additional information
+-- regarding copyright ownership.  The ASF licenses this file
+-- to you under the Apache License, Version 2.0 (the
+-- "License"); you may not use this file except in compliance
+-- with the License.  You may obtain a copy of the License at
+--
+--   http://www.apache.org/licenses/LICENSE-2.0
+--
+-- Unless required by applicable law or agreed to in writing,
+-- software distributed under the License is distributed on an
+-- "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+-- KIND, either express or implied.  See the License for the
+-- specific language governing permissions and limitations
+-- under the License.
+
+-- Exercise Comet's native date_trunc on a timezone that observes DST.
+-- CometTruncTimestamp marks non-UTC as Incompatible, so enable allowIncompatible
+-- to force the native path and verify correctness against Spark.
+
+-- Config: spark.comet.expression.TruncTimestamp.allowIncompatible=true
+-- Config: spark.sql.session.timeZone=America/Los_Angeles
+
+statement
+CREATE TABLE test_trunc_dst(ts timestamp) USING parquet
+
+statement
+INSERT INTO test_trunc_dst VALUES
+  (timestamp('2024-11-03 06:30:00')),
+  (timestamp('2024-11-03 14:30:00')),
+  (timestamp('2024-03-10 05:30:00')),
+  (timestamp('2024-03-10 12:30:00')),
+  (timestamp('2024-11-15 12:00:00')),
+  (timestamp('2024-12-15 23:30:00')),
+  (timestamp('2024-07-15 10:00:00')),
+  (NULL)
+
+-- DAY truncation on a time after fall-back (PST) produces midnight of the same
+-- day, which is BEFORE the fall-back transition and should be in PDT.
+query
+SELECT ts, date_trunc('DAY', ts) FROM test_trunc_dst ORDER BY ts
+
+-- HOUR truncation crossing DST boundaries.
+query
+SELECT ts, date_trunc('HOUR', ts) FROM test_trunc_dst ORDER BY ts
+
+-- WEEK truncation can span DST transitions (the week of Nov 3 2024 starts Oct 28 PDT).
+query
+SELECT ts, date_trunc('WEEK', ts) FROM test_trunc_dst ORDER BY ts
+
+-- MONTH truncation: Nov 15 PST truncated to MONTH gives Nov 1, which is PDT.
+query
+SELECT ts, date_trunc('MONTH', ts) FROM test_trunc_dst ORDER BY ts
+
+-- QUARTER truncation: the motivating case from the PR (Dec PST -> Oct PDT).
+query
+SELECT ts, date_trunc('QUARTER', ts) FROM test_trunc_dst ORDER BY ts
+
+-- YEAR truncation: Dec 15 PST truncated to YEAR gives Jan 1, which is PST too, so no DST crossing.
+query
+SELECT ts, date_trunc('YEAR', ts) FROM test_trunc_dst ORDER BY ts
diff --git a/spark/src/test/resources/sql-tests/expressions/datetime/trunc_timestamp_dst_ambiguous.sql b/spark/src/test/resources/sql-tests/expressions/datetime/trunc_timestamp_dst_ambiguous.sql
new file mode 100644
index 0000000000..a1059736b9
--- /dev/null
+++ b/spark/src/test/resources/sql-tests/expressions/datetime/trunc_timestamp_dst_ambiguous.sql
@@ -0,0 +1,50 @@
+-- Licensed to the Apache Software Foundation (ASF) under one
+-- or more contributor license agreements.  See the NOTICE file
+-- distributed with this work for additional information
+-- regarding copyright ownership.  The ASF licenses this file
+-- to you under the Apache License, Version 2.0 (the
+-- "License"); you may not use this file except in compliance
+-- with the License.  You may obtain a copy of the License at
+--
+--   http://www.apache.org/licenses/LICENSE-2.0
+--
+-- Unless required by applicable law or agreed to in writing,
+-- software distributed under the License is distributed on an
+-- "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+-- KIND, either express or implied.  See the License for the
+-- specific language governing permissions and limitations
+-- under the License.
+
+-- Regression test for ambiguous local times during DST fall-back.
+-- On 2024-11-03 at 2:00 AM America/Los_Angeles, clocks fall back to 1:00 AM,
+-- so 1:30 AM occurs twice (once in PDT, once in PST). Truncating 01:30 to HOUR
+-- gives 01:00, which is ambiguous. chrono's DateTime::with_minute(0) returns
+-- None for ambiguous results, causing a panic in as_micros_from_unix_epoch_utc.
+
+-- Config: spark.comet.expression.TruncTimestamp.allowIncompatible=true
+-- Config: spark.sql.session.timeZone=America/Los_Angeles
+
+statement
+CREATE TABLE test_trunc_ambiguous(ts timestamp) USING parquet
+
+statement
+INSERT INTO test_trunc_ambiguous VALUES
+  (timestamp('2024-11-03 01:30:00'))
+
+query ignore(native panic: chrono returns None for ambiguous local time during DST fall-back)
+SELECT ts, date_trunc('DAY', ts) FROM test_trunc_ambiguous ORDER BY ts
+
+query ignore(native panic: chrono returns None for ambiguous local time during DST fall-back)
+SELECT ts, date_trunc('HOUR', ts) FROM test_trunc_ambiguous ORDER BY ts
+
+query ignore(native panic: chrono returns None for ambiguous local time during DST fall-back)
+SELECT ts, date_trunc('WEEK', ts) FROM test_trunc_ambiguous ORDER BY ts
+
+query ignore(native panic: chrono returns None for ambiguous local time during DST fall-back)
+SELECT ts, date_trunc('MONTH', ts) FROM test_trunc_ambiguous ORDER BY ts
+
+query ignore(native panic: chrono returns None for ambiguous local time during DST fall-back)
+SELECT ts, date_trunc('QUARTER', ts) FROM test_trunc_ambiguous ORDER BY ts
+
+query ignore(native panic: chrono returns None for ambiguous local time during DST fall-back)
+SELECT ts, date_trunc('YEAR', ts) FROM test_trunc_ambiguous ORDER BY ts