Mountain-block groundwater in the Southern Basin-and-Range Province shows a variety of patterns of δ¹⁸O and δ²H that indicate multiple recharge mechanisms. At 2420 m above sea level (masl) in Tucson Basin, seasonal amount-weighted means of δ¹⁸O and δ²H for summer are −8.3, −53‰, and for winter, −10.8 and −70‰, respectively. Elevation-effect coefficients for δ¹⁸O and δ²H are as follows: summer, −1.6 and −7.7 ‰ per km and winter, −1.1 and −8.9 ‰ per km. Little altitude effect exists in 25% of seasons studied. At 2420 masl, amount-weighted monthly averages of δ¹⁸O and δ²H decrease in summer but increase in winter as precipitation intensity increases. In snow-banks, δ¹⁸O and δ²H commonly plots close to the winter local meteoric water line (LMWL). Four principal patterns of (δ¹⁸O, δ²H) data have been identified: (1) data plotting along LMWLs for all precipitation at >1800 masl; (2) data plotting along modified LMWLs for the wettest 30% of months at <1700 masl; (3) evaporation trends at all elevations; (4) other patterns, including those affected by ancient groundwater. Young, tritiated groundwater predominates in studied mountain blocks. Ancient groundwater forms separate systems and mixes with young groundwater. Recharge mechanisms reflect a complex interplay of precipitation season, altitude, precipitation intensity, groundwater age and geology. Tucson Basin alluvium receives mountain-front recharge containing 50%–90% winter precipitation.

Time series of annual Δ¹⁴C and δ¹³C in tree rings ofSequoiadendron giganteum, AD 998–1510, are similar in form. The Δ¹⁴C series completes, with data of Stuiver and Braziunas (1993), a 957-yr time-series. Discrete Fourier transformation of detrended Δ¹⁴C reveals periods of 126, 91, 56, 17.6, 13.6, 10.4, and 7.1 yr. Non-random differences exist between decadal averages of theSequoiadendronΔ¹⁴C data and data of Stuiver and Becker (1993). Periods of 7–17 yr may correspond to Schwabe or related climatic cycles; these have 10–17-yr periods and amplitudes < 6‰ (AD 1100–1250), and periods near 7 yr with amplitudes up to 10‰ (AD 1380–1420). Abrupt increases in Δ¹⁴C are mainly less than 5‰, and do not constitute convincing evidence of increased¹⁴C production from supernovae or solar proton events. The δ¹³C time-series is likely to reflect climate change, and for centennial periodicity lags behind Δ¹⁴C by 20–40 yr (centennial time-scale) and 25–50 yr (millennial). Phase-shifts between solar luminosity and surface Δ¹⁴C are 125–175 yr and 20 yr for millennial and centennial cycles, respectively. The study suggests that strongest climate effects may therefore follow peak luminosity by 125–175 yr for millennial cycles and 20–40 yr for centennial cycles.