In Oracle, how can I detect the date on which daylight savings time begins / ends?

SELECT CHANGEOVER_DATE
FROM SOME_SYSTEM_TABLE
WHERE DATE_TYPE = 'DAYLIGHT_SAVINGS_CHANGEOVER'
  AND TO_CHAR(CHANGEOVER_DATE,'YYYY') = TO_CHAR(SYSDATE,'YYYY');  -- in the current year

Function DaylightSavingTimeStart (p_Date IN Date)
Return Date Is
   v_Date       Date;
   v_LoopIndex  Integer;
Begin
   --Set the date to the 8th day of March which will effectively skip the first Sunday.
   v_Date := to_date('03/08/' || to_char(p_Date,'YYYY') || '02:00:00 AM','MM/DD/YYYY HH:MI:SS PM');
   --Advance to the second Sunday.
   FOR v_LoopIndex IN 0..6 LOOP
      If (RTRIM(to_char(v_Date + v_LoopIndex,'DAY')) = 'SUNDAY') Then
         Return v_Date + v_LoopIndex;
      End If;
   END LOOP;
End;

Function DaylightSavingTimeEnd (p_Date IN Date)
Return Date Is
   v_Date       Date;
   v_LoopIndex  Integer;
Begin
   --Set Date to the first of November this year
   v_Date := to_date('11/01/' || to_char(p_Date,'YYYY') || '02:00:00 AM','MM/DD/YYYY HH:MI:SS PM');
   --Advance to the first Sunday
   FOR v_LoopIndex IN 0..6 LOOP
      If (RTRIM(to_char(v_Date + v_LoopIndex,'DAY')) = 'SUNDAY') Then
         Return v_Date + v_LoopIndex;
      End If;
   END LOOP;
End;

ALTER SESSION SET time_zone='America/Phoenix';
DROP TABLE TimeDifferences;
CREATE TABLE TimeDifferences(LocalTimeZone TIMESTAMP(0) WITH LOCAL TIME ZONE);
INSERT INTO TimeDifferences
(
   SELECT to_date('01/01/' || to_char(sysdate-365,'YYYY') || '12:00:00','MM/DD/YYYYHH24:MI:SS')+rownum-1
   FROM dual CONNECT BY rownum<=365
);
COMMIT;

ALTER SESSION SET time_zone='America/Edmonton';
SELECT LocalTimeZone-1 DaylightSavingTimeStartAndEnd
FROM
(
   SELECT LocalTimeZone,
      to_char(LocalTimeZone,'HH24') Hour1,
      LEAD(to_char(LocalTimeZone,'HH24')) OVER (ORDER BY LocalTimeZone) Hour2
   FROM TimeDifferences
)
WHERE Hour1 <> Hour2;