Pilot reported flying right pattern at smn is unsafe; after misinterpreting chart symbology.

Attributes
ACN	1668729
Time
Date	201907
Local Time Of Day	1201-1800
Place
Locale Reference	SMN.Airport
State Reference	ID
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	Part 91
Flight Phase	Initial Approach
Route In Use	Visual Approach
Flight Plan	None
Person 1
Function	Single Pilot Pilot Flying
Qualification	Flight Crew Flight Instructor Flight Crew Flight Engineer Flight Crew Air Transport Pilot (ATP) Flight Crew Instrument Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 30 Flight Crew Total 27000 Flight Crew Type 50
Events
Anomaly	No Specific Anomaly Occurred All Types

Narrative:

The sectional chart that lemhi county (smn); salmon; identification shows rp* for the airport which requires referencing the airport supplement. Rp* for smn means 'right pattern runway 35 at night'. If a pilot flies a right pattern for runway 35; even in the daytime they are faced with rising (in my opinion rapidly rising) terrain while descending on the downwind and base legs. This is worrisome even in daylight hours. At night; a pilot unfamiliar with the terrain could easily be put in jeopardy on this approach. However; they would be following the guidance of the sectional chart and airport supplement.I would like to know the rationale for a right pattern to runway 35; day or night. The terrain west of smn is much more open and forgiving.

Original NASA ASRS Text

Title: Pilot reported flying right pattern at SMN is unsafe; after misinterpreting chart symbology.

Narrative: The Sectional Chart that Lemhi County (SMN); Salmon; ID shows RP* for the airport which requires referencing the Airport Supplement. RP* for SMN means 'Right Pattern Runway 35 AT NIGHT'. If a pilot flies a right pattern for runway 35; even in the daytime they are faced with rising (in my opinion rapidly rising) terrain while descending on the downwind and base legs. This is worrisome even in daylight hours. At night; a pilot unfamiliar with the terrain could easily be put in jeopardy on this approach. However; they would be following the guidance of the Sectional Chart and Airport Supplement.I would like to know the rationale for a right pattern to runway 35; DAY or NIGHT. The terrain west of SMN is much more open and forgiving.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.