A Look Inside the Data: Daily Precipitation Record

Today’s dataset is from Chapter 4, part 8 of the Report of Sacramento-San Joaquin Water Supervision for year 1941. Table 113 is a daily record of precipitation logged at Llano Seco Rancho throughout the year of 1941. Llano Seco Rancho is located in Butte County just North of Sacramento. The table shows that the driest months in California are consistently June to September. I plan to explain the significance of the data, but first I wanted to look into more about the ranch.

Llano Seco Rancho

Llano Seco means dry land in Spanish. The Sacramento River and Chico Creek provide the ranch with valuable water . The land is located at the base of the Sierra Mountains and is now a major cultivator of livestock and wheat. Now to examine the data!

The Table

Chapter 4, part 8 from Report of Sacramento-San Joaquin Water Supervision for year 1941 page 160.

Table 113 is similar to other tables in Chapter 4. The location is provided in the title of the table and days 1-31 are listed in the left column. The months serve as the header for the table, and the lack of data in the table is more telling than the presence of data. Gaps in the table let us know no rain was collected on that day while the entire months of July and August are completely dry. The data comes from the United States Weather Bureau.


The tables in Report of Sacramento-San Joaquin Water Supervision show a significant drop in precipitation between the months of June and September. According to Drought.gov, California is the driest between May and October. These early reports on precipitation and water provisions provide useful data for researchers examining drought management in California.